fix(datasource): map combined_list to can_read so Gamma can list datasets

The combined_list endpoint added in #37815 used the auto-derived
`can_combined_list on Datasource` permission, which is not in
READ_ONLY_PERMISSION and is therefore excluded from the Gamma role by
_is_alpha_only. Map it to `can_read on Datasource` instead so Gamma
inherits access alongside Alpha and Admin.

superset/datasource/api.py

@@ -42,6 +42,10 @@ class DatasourceRestApi(BaseSupersetApi):
     class_permission_name = "Datasource"
     resource_name = "datasource"
     openapi_spec_tag = "Datasources"
+    # Map the combined list endpoint to the generic `can_read on Datasource`
+    # permission so it inherits the Gamma/Alpha/Admin grants instead of
+    # creating a method-specific permission that is Alpha-only by default.
+    method_permission_name = {"combined_list": "read"}
 
     @expose(
         "/<datasource_type>/<int:datasource_id>/column/<column_name>/values/",

tests/integration_tests/datasource/api_tests.py

@@ -212,10 +212,8 @@ class TestDatasourceApi(SupersetTestCase):
         run_mock,
         can_access_mock,
     ):
-        security_manager.add_permission_view_menu("can_combined_list", "Datasource")
-        perm = security_manager.find_permission_view_menu(
-            "can_combined_list", "Datasource"
-        )
+        security_manager.add_permission_view_menu("can_read", "Datasource")
+        perm = security_manager.find_permission_view_menu("can_read", "Datasource")
         admin_role = security_manager.find_role("Admin")
         security_manager.add_permission_role(admin_role, perm)
         can_access_mock.side_effect = [True, True]