Limit concurrency of update-manifest workflow to 1

Author: luhenry

.github/workflows/update-manifest.yml

@@ -13,6 +13,10 @@ defaults:
   run:
     shell: bash --noprofile --norc -euxo pipefail {0}
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
+
 jobs:
   update:
     runs-on: ubuntu-latest