cicd: run build-snapshot against prs

.github/workflows/build-snapshot.yml

@@ -2,8 +2,10 @@
 name: "Build Snapshot"
 
 on:
-  - push
-  - workflow_dispatch
+  push:
+  workflow_dispatch:
+  pull_request:
+    branches: [main]
 
 jobs:
   build-snapshot: