workflows/{merge-group,pr}: avoid posting "no PR failures" for pull_request trigger

The required status checks should depend on exactly one workflow,
triggered via pull_request_target or merge_group. Anything that is
triggered by pull_request is for testing purposes of the workflows
themselves only.

.github/workflows/merge-group.yml

@@ -29,6 +29,7 @@ jobs:
   # This job's only purpose is to create the target for the "Required Status Checks" branch ruleset.
   # It "needs" all the jobs that should block the Merge Queue.
   unlock:
+    if: github.event_name != 'pull_request'
     # Modify this list to add or remove jobs from required status checks.
     needs:
       - lint

.github/workflows/pr.yml

@@ -122,6 +122,7 @@ jobs:
   # This job's only purpose is to create the target for the "Required Status Checks" branch ruleset.
   # It "needs" all the jobs that should block merging a PR.
   unlock:
+    if: github.event_name != 'pull_request'
     # Modify this list to add or remove jobs from required status checks.
     needs:
       - check