Run push builds only on master

The workflow triggers on both push and pull_request without branch
filters, so every PR from a repository branch runs the full matrix
twice. Limiting the push trigger to master keeps a single run per PR
plus a post-merge run.

Author: guillaume-sainthillier

.github/workflows/unit-tests.yaml

@@ -3,6 +3,7 @@ name: "Unit Tests"
 on:
     pull_request:
     push:
+        branches: [master]
     workflow_dispatch:
 
 jobs: