ci: update main workflow concurrency and triggers

Author: felangel

.github/workflows/main.yaml

@@ -1,6 +1,16 @@
 name: very_good_test_runner
 
-on: pull_request
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
 
 jobs:
   build: