CI: do not run build and test actions twice on PRs

Author: pazz

.github/workflows/build.yml

@@ -1,5 +1,11 @@
 name: Build
-on: [push, pull_request] 
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
 
 jobs: 
   build: 

.github/workflows/test.yml

@@ -1,5 +1,11 @@
 name: Test
-on: [push, pull_request] 
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
 
 jobs: 
   test: