Revert "Temporarily add push trigger to ci-nightly.yml for testing"

This reverts commit d29bc34.

Author: leofang

.github/workflows/ci-nightly.yml

@@ -16,10 +16,6 @@ concurrency:
   cancel-in-progress: true
 
 on:
-  push:
-    branches:
-      - "main"
-      - "pull-request/[0-9]+"
   schedule:
     # 2:17 AM UTC daily, after the midnight main CI build finishes.
     # Avoid minute 0 because GitHub documents high scheduled-workflow load