chore: changed how PRs trigger build pipeline

.github/workflows/build.yml

@@ -3,7 +3,7 @@ on:
   push:
   pull_request:
     branches:
-      - "**"
+      - "main"
 
 # This is the example from the readme.
 # On each push to the `main` branch it will create or update a GitHub build, build your app, and upload the artifacts to the build.