Update flake8.yml

Author: ikostan

.github/workflows/flake8.yml

@@ -2,7 +2,10 @@
 name: "Flake8"
 
 on:   # yamllint disable-line rule:truthy
-  workflow_call:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
 
 permissions:
   contents: "read"