chore(main): check paths diff within same branch on push

[rebornplusplus]

Proposed changes

On "push" events, specify the "base" value of dorny/paths-filter action. This ensures that the comparison is made against the recent commit on that particular branch before pushing the new commits.

Previously, it was left empty, resulting in the default value which is the default branch "ubuntu-22.04". Thus pushed to the "ubuntu-24.04" branch would be compared with "ubuntu-22.04" which is a bug. [1]

This commit fixes said bug.

[1] https://github.com/canonical/chisel-releases/actions/runs/8092571514/job/22113523205#step:3:52

Testing

Expected behaviour on Push:

• Changes will be computed between recent commits before push and after push: https://github.com/rebornplusplus/chisel-releases/actions/runs/8094448190/job/22119167199 (Check the logs of "Check changed paths" step)

  Changes will be detected between 52fd99d and ubuntu-24.04

Expected behaviour on PRs:

• Nothing changes: https://github.com/rebornplusplus/chisel-releases/actions/runs/8094398023/job/22119019184

Checklist

• I have read the contributing guidelines
• I have already submitted the CLA form

[rebornplusplus]

Note that the failing tests in this PR will be fixed by #158.

[cjdcordeiro]

I appreciate that this works, but given that we have branch moderation, PR tests and scheduled (cron) full-release tests, I actually think it is better to just remove the push event on the ubuntu branches. makes everything simpler without sacrificing the testing. The worst thing that can happen is a delay:

• someone with admin rights pushes directly to a branch, bypassing the rules (which shouldn't be done anyway)
• there will be no tests running right away, but there will be the scheduled tests anyway later on

[rebornplusplus]

Closing this in favour of #172, #173, #174 and #175. We need to open this if we ever bring back on: push workflows.