fix(github): do not skip scheduled labeler runs

Author: rubenhoenle

.github/workflows/labeler.yaml

@@ -8,17 +8,44 @@ on:
     - cron: '0 * * * *'
 
 jobs:
-  labeler:
+  # this job runs when the workflow was triggered by the 'pull_request' event
+  pr-labeler:
     permissions:
       contents: read
       pull-requests: write
       issues: write
     # don't run on PRs from forks (token has no write permissions)
-    if: ${{ github.event.pull_request.head.repo.full_name == github.repository }}
+    if: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name == github.repository }}
     name: "Labeler"
     runs-on: ubuntu-latest
     steps:
       - name: Labeler action
         uses: actions/labeler@v7
         with:
           sync-labels: false
+  
+  # This job runs when the workflow was triggered by the 'workflow_dispatch' or the 'schedule' event.
+  # This is neccessary because for PRs from forks the default short-lived GitHub token has no write permissions
+  # and can not add labels to the PR therefore. This means we have to label all PRs from forks using the 'schedule' event.
+  scheduled-labeler:
+    permissions:
+      contents: read
+      pull-requests: write
+      issues: write
+    # don't run on PRs from forks (token has no write permissions)
+    if: ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' }}
+    name: "Label all open PRs"
+    runs-on: ubuntu-latest
+    steps:
+      - name: Fetch open PR numbers
+        id: fetch-prs
+        run: |
+          numbers=$(gh pr list --repo ${{ github.repository }} --state open --limit 500 --json number --jq '.[].number')
+          echo numbers=$numbers >> $GITHUB_OUTPUT
+
+      - name: Labeler action
+        if: ${{ steps.fetch-prs.outputs.numbers != '' }}
+        uses: actions/labeler@v7
+        with:
+          sync-labels: false
+          pr-number: ${{ steps.fetch-prs.outputs.numbers }}