Avoid duplicate CI runs on feature branches with open PRs

Restrict push trigger to master and version tags only. Feature branches
are covered by the pull_request trigger.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: DreierF

.github/workflows/actions.yml

@@ -2,7 +2,7 @@ name: Build
 
 on:
   push:
-    branches: '**'
+    branches: master
     tags: 'v*'
   pull_request:
     branches: '**'