🧪 Disallow PRs against non-default branches

Author: webknjaz

.github/workflows/reusable-smoke-test.yml

@@ -26,6 +26,19 @@ env:
     PYTEST_THEME_MODE
 
 jobs:
+  legit-pr:
+
+    runs-on: ubuntu-latest
+
+    timeout-minutes: 1
+
+    steps:
+    - name: Fail on PRs against illegal branches
+      if: >-
+        github.event_name == 'pull_request'
+        && github.ref_name == github.event.repository.default_branch
+      run: exit 1
+
   fail-fast:
 
     strategy: