fix: merge main workflow credentials (#1274)

Author: 0marperez

.github/workflows/merge-main.yml

@@ -11,4 +11,5 @@ jobs:
       - name: Merge main
         uses: awslabs/aws-kotlin-repo-tools/.github/actions/merge-main@main
         with:
+          ci-user-pat: ${{ secrets.CI_USER_PAT }}
           exempt-branches: # Add any if required