Building for main branch only

.github/workflows/build.yml

@@ -1,5 +1,9 @@
 name: "FAP: Build for multiple SDK sources"
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
 jobs:
   ufbt-build-action:
     runs-on: ubuntu-latest