feat: trigger link checker on pull requests

Author: JeelRajodiya

.github/workflows/link-checker.yml

@@ -2,6 +2,7 @@ name: Link Checker
 
 on:
   repository_dispatch:
+  pull_request:
   workflow_dispatch:
   schedule: 
     - cron: '0 0 1 * *' # Run at midnight on the first of every month