chore(gha): fix cron command

Author: sanjayankur31

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
   pull_request:
     branches: [ master, development, experimental  ]
   schedule:
-    - cron '0 4 1,15 * *'  # 4 am on 1st and 15th of each month
+    - cron: '0 4 1,15 * *'  # 4 am on 1st and 15th of each month
 
 jobs:
   build: