Add a GitHub Actions workflow to automatically sync the repository la…

…bels.

This commit adds a `.github/workflow/sync-labels.yml` file, which defines a workflow that syncs this repository's labels with the contents of the `.github/labels.yml` file. The labels are synced automatically whenever the `.github/labels.yml` file changes.

.github/workflows/sync-labels.yml

@@ -7,7 +7,7 @@ on:
       - .github/labels.yml
       - .github/workflows/sync-labels.yml
   schedule:
-    - cron: 0 0 1 * *
+    - cron: 6 6 6 * *
   workflow_dispatch:
 
 jobs: