Protect build cleanup from unsafe output paths

.github/workflows/run-unit-tests.yml

@@ -91,6 +91,9 @@ jobs:
       - name: Run Unit Tests
         run: pio test -e native -e native_kiss_modem -vv
 
+      - name: Verify build output cleanup safety
+        run: python3 -B test/test_build_output_safety.py -v
+
       - name: Verify serial mOTA response deadlines and RX fairness
         run: python3 -B test/test_mota_serial_deadline.py -v