core -> common testing

[emmyoop]

resolves #18

Description

Adds workflow to test specific dbt-core branches against specific dbt-common branches.

• can be triggered:
  • manually
  • via a workflow
  • on merge
  • on pull_request - only runs unit tests

We only run unit tests on pull requests to reduce the time it takes to test. The entire core test suite will run on merge to ensure nothing is broken before fully merging into main.

Also adds stub for scheduled testing with alerts in slack on failures. Test will be added in #62 once proper auths are in place.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (af14523) 51.47% compared to head (bda211e) 51.47%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #54   +/-   ##
=======================================
  Coverage   51.47%   51.47%           
=======================================
  Files          49       49           
  Lines        2856     2856           
=======================================
  Hits         1470     1470           
  Misses       1386     1386           

Flag	Coverage Δ
unit	51.47% <ø> (ø)

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[MichelleArk]

Looks really good! Should we expect the on-merge integration tests to run as soon as we merge this, or should we test that in a follow-up?

[emmyoop]

@MichelleArk I believe in the follow up. It's why i haven't pushed for a review of #51 - saving it to test the on merge functionality.