Update Check_file_size.yml

.github/workflows/Check_file_size.yml

@@ -1,6 +1,6 @@
 name: Check file size
 on:               # or directly `on: [push]` to run the action on every push on any branch
-  push:
+  pull_request:
     branches: [main]
 
   # to run this workflow manually from the Actions tab