GitHub Actions Safari runs not labelled with master

[gsnedders]

This excludes them from the default view, see e.g. https://staging.wpt.fyi/results/?run_id=6174988006588416

The problem lies in:

wpt.fyi/api/ghactions/notify.go

Lines 178 to 184 in d6339c4

	if (*workflowRun.Event == "push" &&
	*workflowRun.HeadRepository.Owner.Login == owner &&
	*workflowRun.HeadRepository.Name == repo) &&
	(*workflowRun.HeadBranch == "master" ||
	epochBranchesRegex.MatchString(*workflowRun.HeadBranch)) {
	labels.Add(shared.MasterLabel)
	}

We're both checking that the event is push (it isn't, it's workflow_run after web-platform-tests/wpt@2419936), and the head branch the workflow run is triggered against is actually mostly irrelevant (see web-platform-tests/wpt#48659; we need to manually checkout the right ref to actually run what we want to).

Without this in the workflow_run payload, we don't actually have an easy way to pass what we're actually running against to wpt.fyi. We could maybe add this to what we upload to notify wpt.fyi, but that clearly has security considerations (though maybe if we're running against master on the right repo we can trust what we upload?).

An easy-but-bad temporary fix is to just label every workflow_run with master, which is currently true because we should only ever be running things that are on master in that case. This might be worthwhile to unblock this?

(See also #4020, given this is now the thing stopping the runs from showing up by default.)