Do not try to remove stale label on PRs (#5292)

.github/workflows/stale.yml

@@ -23,14 +23,17 @@ jobs:
           days-before-stale: 30
           days-before-close: 5
           stale-issue-message: 'This issue is stale because it has been open 30 days with no activity. Please comment or update this issue or it will be closed in 5 days.'
-          stale-issue-label: $stale_label
+          stale-issue-label: '${{ env.stale_label }}'
           exempt-issue-labels: 'Internal, Fixed in next release, Bug: Confirmed, Documentation Needed'
           exempt-all-issue-assignees: true
           operations-per-run: 300
           close-issue-reason: 'not_planned'
 
-  remove_stale: # trigger "stale" removal immediately when stale issues are commented on
-    if: github.event_name == 'issue_comment'
+  remove_stale:
+    # trigger "stale" removal immediately when stale issues are commented on
+    # we need to explicitly check that the trigger does not run on comment on a PR as
+    # https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#issue_comment-on-issues-only-or-pull-requests-only
+    if: ${{ !github.event.issue.pull_request && github.event_name != 'schedule' }}
     permissions:
       contents: read #  for actions/checkout
       issues: write #  to edit issues label
@@ -39,7 +42,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v3.5.2
       - name: Remove 'stale' label
-        run: gh issue edit ${{ github.event.issue.number }} --remove-label $stale_label
+        run: gh issue edit ${{ github.event.issue.number }} --remove-label ${{ env.stale_label }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}