fix(worflows): add back checkout step for PR labelling

This was removed because the upstream example config does not have it,
but since we override the size buckets, we need to check out the code
to make the override config available.

.github/workflows/label-pr-size.yml

@@ -10,6 +10,8 @@ jobs:
       contents: write
       pull-requests: write
     steps:
+      - name: Fetch code
+        uses: actions/checkout@v7
       - name: Label and comment PR
         uses: boschresearch/pr-size-labeler@v5
         # Uncomment these lines if you want to use your own custom configuration