Don't run update release branch workflow on forks.

.github/workflows/update-release-branch.yml

@@ -12,6 +12,7 @@ on:
 jobs:
   update:
     runs-on: ubuntu-latest
+    if: ${{ github.repository == 'github/codeql-action' }}
     steps:
     - uses: actions/checkout@v2
       with: