📝 (deadlink_checker.yml): change default branch name from 'master' to…

… 'main' to align with updated naming conventions

🔧 (deadlink_checker.yml): update cron schedule to run the job everyday at 9:00 AM for deadlink checking process

.github/workflows/deadlink_checker.yml

@@ -3,10 +3,11 @@ name: Check Markdown links
 on:
   push:
     branches:
-    - master
+      - main
+  pull_request:
   schedule:
-  # Run everyday at 9:00 AM (See https://pubs.opengroup.org/onlinepubs/9699919799/utilities/crontab.html#tag_20_25_07)
-  - cron: "*/5 * * * *"
+    # Run everyday at 9:00 AM (See https://pubs.opengroup.org/onlinepubs/9699919799/utilities/crontab.html#tag_20_25_07)
+    - cron: "0 9 * * *"
 
 jobs:
   markdown-link-check: