Avoid duplicate GH Actions runs for PRs

Author: johnpaulett

.github/workflows/test.yaml

@@ -1,6 +1,9 @@
 name: tests
 
-on: [push, pull_request]
+on:
+  push:
+    branches: [main]
+  pull_request:
 
 env:
   primary-python-version: "3.12"