Remove silliness with two separate CI runs

Was previously there because DJRF required pytz

.github/workflows/ci.yml

@@ -155,17 +155,7 @@ jobs:
           POSTGRES_DB: postgres
           POSTGRES_USER: postgres
           POSTGRES_PASSWORD: postgres
-        run: poetry run pytest --cov=timezone_field --ignore=tests/test_serializer_field.py
-
-      - name: Test serializer fiels with coverage
-        if: matrix.tz-engine == 'pytz'
-        env:
-          POSTGRES_HOST: localhost
-          POSTGRES_PORT: 5432
-          POSTGRES_DB: postgres
-          POSTGRES_USER: postgres
-          POSTGRES_PASSWORD: postgres
-        run: poetry run pytest --cov=timezone_field tests/test_serializer_field.py
+        run: poetry run pytest --cov=timezone_field
 
       - name: Generate coverage report
         run: poetry run coverage xml