ci: measure coverage and fail below 50%

The test step runs under coverage and reports files that are not fully
covered. pyproject.toml holds the configuration and the floor: 51%
measured without the live libvirt suite on 2026-10-03, floor 50% to
absorb differences between Python versions. With the live suite against
a real host the same code is 69% covered.

.github/workflows/test.yml

@@ -56,9 +56,11 @@ jobs:
       - name: Run Django Migrations
         run: python manage.py migrate --noinput
 
-      # Includes the vrtManager tests
+      # Includes the vrtManager tests; fails below the coverage floor in pyproject.toml
       - name: Run Test Suite
-        run: python manage.py test
+        run: |
+          coverage run manage.py test
+          coverage report --skip-covered
 
       - name: Validate OpenAPI Schema
         run: python manage.py spectacular --validate --fail-on-warn --file /dev/null