Run link checker GitHub action on schedule. (#1221)

Most PRs do not add/update links, however sites go down often. This change makes sure that we catch any broken link in the repository and fix it, but at the same time we do not want to block PRs because of some unrelated broken links.

This PR updates the workflow to run everyday at midnight UTC.

Signed-off-by: Rabi Panda <adnapibar@gmail.com>

.github/workflows/links.yml

@@ -1,10 +1,7 @@
 name: Link Checker
 on:
-  push:
-    branches: [ main ]
-  pull_request:
-    branches: [ main ]
-
+  schedule:
+    - cron:  '0 0 * * *'
 jobs:
   linkchecker: