Fix workflows to not double run

.github/workflows/build.yaml

@@ -1,5 +1,8 @@
 name: build
-on: [ push, pull_request ]
+on:
+  push:
+    branches: [ main ]
+  pull_request:
 jobs:
   build:
     runs-on: ubuntu-latest

.github/workflows/test.yaml

@@ -1,5 +1,8 @@
 name: test
-on: [ push, pull_request ]
+on:
+  push:
+    branches: [ main ]
+  pull_request:
 jobs:
   test:
     runs-on: ubuntu-latest