Add a label to the PR when one is defined.

Author: desrosj

.github/workflows/backport.yml

@@ -277,10 +277,14 @@ jobs:
             PR_HEAD="${STEPS_BACKPORT_BRANCH_OUTPUTS_NAME}"
           fi
 
-          gh pr create \
+          PR_URL=$(gh pr create \
             --repo "${PR_REPO}" \
             --base "${MATRIX_BRANCH}" \
             --head "${PR_HEAD}" \
             --title "$PR_TITLE" \
             --assignee "${GITHUB_ACTOR}" \
-            --body "$(echo -e "$BODY")"
+            --body "$(echo -e "$BODY")")
+
+          if gh label list --repo "${PR_REPO}" --json name --jq '[.[].name] | contains(["Auto-backport"])' | grep -q 'true'; then
+            gh pr edit "$PR_URL" --repo "${PR_REPO}" --add-label 'Auto-backport'
+          fi