指定只有main更新时才部署pages (#15)

* 指定只有main更新时才部署pages

.github/workflows/build.yml

@@ -1,5 +1,10 @@
 name: Build and Deploy
-on: [ push, pull_request ]
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
 jobs:
   build-and-deploy:
     runs-on: ubuntu-latest