Don't block merges on linkcheck

[woodruffw]

I believe this was an oversight in #2035 -- it doesn't make sense to allow linkchecks to pass PR gates, only to bounce them at the merge group.

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📚 Documentation preview 📚: https://python-packaging-user-guide--2128.org.readthedocs.build/en/2128/

[woodruffw]

I had to widen this to non-main pushes as well, since first-party PRs will also trigger this since they receive the push event.

[webknjaz]

Suggested change

	(github.event_name == 'push' && github.ref != 'refs/heads/main')) }}
	(github.event_name == 'push' && github.ref_name != github.event.repository.default_branch)) }}

[webknjaz]

Something like this seems nicer

Suggested change

	${{ toJSON(github.event_name == 'pull_request' || github.event_name == 'merge_group' ||
	${{ toJSON(contains(['merge_group', 'pull_request'], github.event_name) ||

[webknjaz]

since first-party PRs will also trigger this since they receive the push event.

Not sure we really need to care about pushes, though. What fails is merge queue events.

[woodruffw]

since first-party PRs will also trigger this since they receive the push event.

Not sure we really need to care about pushes, though. What fails is merge queue events.

FWICT the merge queue only becomes available after the push-triggered checks succeed, since the linkcheck is marked as required on that trigger still.