ci(weekly-update): add concurrency group to prevent overlapping runs

Use cancel-in-progress: false so a scheduled run doesn't abort a
long-running one (weekly update takes 10+ minutes and creates a PR).

Author: jdalton

.github/workflows/weekly-update.yml

@@ -15,6 +15,10 @@ on:
 permissions:
   contents: read
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
+
 jobs:
   check-updates:
     name: Check for dependency updates