chore(cts): execute cts every six hours

.github/workflows/run_cts_tests.yaml

@@ -1,11 +1,12 @@
 name: Compatibility Test Suite
 
 on:
+  schedule:
+    - cron:  '0 */6 * * *'
   push:
     tags:
       - v*
       - e*
-  pull_request:
 
 jobs:
   ldap: