prevent data race in testing artifact fetcher

[leehinman]

What does this PR do?

Switch from uint64 to an atomic.Uint64 to prevent data race in testing artifact fetcher

Why is it important?

In CI we can see the data race:

==================
WARNING: DATA RACE
Read at 0x00c0002dbc18 by goroutine 11:
  github.com/elastic/elastic-agent/pkg/testing.(*writeProgress).printProgress()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:285 +0x158
  github.com/elastic/elastic-agent/pkg/testing.newWriteProgress.func1()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:267 +0x4c

Previous write at 0x00c0002dbc18 by goroutine 9:
  github.com/elastic/elastic-agent/pkg/testing.(*writeProgress).Write()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:273 +0x50
  io.(*teeReader).Read()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/io/io.go:615 +0xac
  io.copyBuffer()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/io/io.go:427 +0x1ec
  io.Copy()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/io/io.go:386 +0x74
  os.genericReadFrom()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/os/file.go:161 +0x2c
  os.(*File).ReadFrom()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/os/file.go:155 +0x2b0
  io.copyBuffer()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/io/io.go:413 +0x154
  io.Copy()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/io/io.go:386 +0x398
  github.com/elastic/elastic-agent/pkg/testing.DownloadPackage()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:243 +0x320
  github.com/elastic/elastic-agent/pkg/testing.(*artifactResult).Fetch()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:110 +0x284
  github.com/elastic/elastic-agent/pkg/testing.TestArtifactFetcher_SnapshotOnly()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact_test.go:95 +0xa10
  testing.tRunner()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1576 +0x180
  testing.(*T).Run.func1()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1629 +0x40

Goroutine 11 (running) created at:
  github.com/elastic/elastic-agent/pkg/testing.newWriteProgress()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:267 +0x168
  github.com/elastic/elastic-agent/pkg/testing.DownloadPackage()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:237 +0x268
  github.com/elastic/elastic-agent/pkg/testing.(*artifactResult).Fetch()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact.go:110 +0x284
  github.com/elastic/elastic-agent/pkg/testing.TestArtifactFetcher_SnapshotOnly()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/src/github.com/elastic/elastic-agent/pkg/testing/fetcher_artifact_test.go:95 +0xa10
  testing.tRunner()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1576 +0x180
  testing.(*T).Run.func1()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1629 +0x40

Goroutine 9 (running) created at:
  testing.(*T).Run()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1629 +0x5b4
  testing.runTests.func1()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:2036 +0x80
  testing.tRunner()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1576 +0x180
  testing.runTests()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:2034 +0x6a8
  testing.(*M).Run()
      /var/lib/jenkins/workspace/tic-agent_elastic-agent-mbp_8.11/.gvm/versions/go1.20.10.linux.arm64/src/testing/testing.go:1906 +0x8e0
  main.main()
      _testmain.go:59 +0x2b8
==================

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Author's Checklist

How to test this PR locally

go test -v -race ./pkg/testing -run TestArtifactFetcher_SnapshotOnly -count 10000

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Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[mergify]

This pull request does not have a backport label. Could you fix it @leehinman? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

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• Start Time: 2023-11-02T13:45:28.272+0000

• Duration: 16 min 3 sec

❕ Flaky test report

No test was executed to be analysed.

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[cmacknz]

Merge in main to get past the buildkite failure

[cmacknz]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated

[cmacknz]

buildkite test it

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