ci(build.yaml): add a guard step to skip builds for PRs targeting master or dev branches

.gitea/workflows/build.yaml

@@ -4,6 +4,9 @@ on: pull_request
 
 jobs:
   build:
+    # Skip if PR base is master/dev
+    if: github.base_ref != 'master' && github.base_ref != 'dev'
+
     runs-on: ubuntu-latest
 
     steps: