CI: skip build/test jobs if only Docs/ is modified

[EZoni]

Could we do this to make sure that we run the GitHub Actions and Azure jobs (build, test) only if at least one file outside the Docs directory is modified, i.e., skip those jobs if only files in the Docs directory are modified?

I think it would be safe to do so (and a bit of a waste of resources to not do so...), but I leave it open for discussion.

If merged, we could test this rebasing #5386 and seeing if the correct CI jobs are skipped.

Note that this PR leaves the other CI jobs untouched, e.g., source, docs, CodeQL, etc.

[WeiqunZhang]

Good idea!

[lucafedeli88]

Excellent idea! I fully agree

[ax3l]

Nice!! 🤩

[EZoni]

Note that this is handled by GitHub Actions in a way that is not optimal.

From their docs (https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/collaborating-on-repositories-with-code-quality-features/troubleshooting-required-status-checks#handling-skipped-but-required-checks):

Warning: If a workflow is skipped due to path filtering, branch filtering or a commit message, then checks associated with that workflow will remain in a "Pending" state. A pull request that requires those checks to be successful will be blocked from merging.

The GitHub Actions workflows that we skip will appear as "pending". This should be fine for now, as maintainers should be able to force-merge the PR anyways. Hopefully GitHub will fix this in the future, marking the workflows that are skipped as "skipped" rather than "pending". I can think of other work-arounds in the meantime.