workflows/pr: fix condition for no-pr-failures job

The `cancelled()` condition seems to only apply when *the whole
workflow* was cancelled. This is not the case when a single job is
cancelled due to timeout.

We can replicate this by checking each needs.result manually.

.github/workflows/pr.yml

@@ -160,7 +160,11 @@ jobs:
     # Do NOT change the name of this job, otherwise the rule will not catch it anymore.
     # This would prevent all PRs from merging.
     name: no PR failures
-    if: ${{ cancelled() || failure() }}
+    # A single job is "cancelled" when it hits its timeout. This is not the same
+    # as "skipped", which happens when the `if` condition doesn't apply.
+    # The "cancelled()" function only checks the whole workflow, but not individual
+    # jobs.
+    if: ${{ failure() || contains(needs.*.result, 'cancelled') }}
     runs-on: ubuntu-24.04-arm
     steps:
       - run: exit 1