test: add data.py to acceptable isolated app imports

Per OEP-49, both api.py and data.py are allowed to be imported into
other apps:

https://open-edx-proposals.readthedocs.io/en/latest/best-practices/oep-0049-django-app-patterns.html#api-py

setup.cfg

@@ -183,9 +183,10 @@ isolated_apps =
     openedx.core.djangoapps.xblock
     openedx.core.lib.xblock_serializer
 allowed_modules =
-    # Only imports from api.py are allowed elsewhere in the code
+    # Only imports from api.py and data.py are allowed elsewhere in the code
     # See https://open-edx-proposals.readthedocs.io/en/latest/best-practices/oep-0049-django-app-patterns.html#api-py
     api
+    data
 
 [importlinter:contract:3]
 name = Do not import apps from openedx-learning (only import from openedx_learning.api.* and openedx_learning.lib.*).