Run link checker weekly

Author: rly

.github/workflows/link-check.yml

@@ -2,6 +2,9 @@
 name: Link Check Source Files with Lychee
 
 on:
+  # Runs weekly every Sunday at 05:00 UTC (midnight EST)
+  schedule:
+    - cron: '0 5 * * 0'
   # Runs on pull requests targeting the dev branch
   pull_request:
     branches: ["dev"]