misc: only run release branch workflow on public repo

Author: 0marperez

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

@@ -29,6 +29,8 @@ env:
 
 jobs:
   update-release:
+    # Mirror repo doesn't have a release branch
+    if: github.repository == 'awslabs/aws-sdk-kotlin'
     runs-on: ubuntu-latest
     steps:
       - name: Set start timestamp