Call build_artifact_comment.yml only for PRs

[3nids]

This will avoid false negative workflow failures

[m-kuhn]

confirmed in external repo, according to @3nids

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit c04271f)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit c04271f)

[nyalldawson]

This actually breaks the workflow -- see #59555 .

[3nids]

This workflow would have fail before because there is no zip available since it's on the 3.34 release branch which has no win Qt6 builds.
We can fine tune more by blacklisting some branches.

[nyalldawson]

@3nids it's missing the test failure report, that's what I'm wanting

[3nids]

@nyalldawson the test failure is brought by the other workflow (https://github.com/qgis/QGIS/blob/master/.github/workflows/write_failure_comment.yml) which I didn't touch and I don't think they depend on each other. Or am I missing something?
Anyway, we can revert if you think that helps.