only build either push or pull_request triggers, not both

Author: altendky

.github/workflows/lint_python.yml

@@ -1,5 +1,13 @@
 name: lint_python
-on: [pull_request, push]
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - '**'
+
 jobs:
   lint:
     runs-on: ubuntu-latest