Made runtests.py run gis_tests only when using a GIS database backend.

This facilitates other changes like refs #28160.

tests/gis_tests/gis_migrations/test_commands.py

@@ -1,9 +1,8 @@
 from django.core.management import call_command
 from django.db import connection
-from django.test import TransactionTestCase, skipUnlessDBFeature
+from django.test import TransactionTestCase
 
 
-@skipUnlessDBFeature("gis_enabled")
 class MigrateTests(TransactionTestCase):
     """
     Tests running the migrate command in Geodjango.