refactor: update migration paths and improve database operation handling

backend/tests/test_organizations_member_remove_api.py

@@ -36,6 +36,10 @@ class _FakeSession:
     committed: int = 0
 
     async def exec(self, _statement: Any) -> Any:
+        is_dml = _statement.__class__.__name__ in {"Delete", "Update", "Insert"}
+        if is_dml:
+            self.executed.append(_statement)
+            return None
         if not self.exec_results:
             raise AssertionError("No more exec_results left for session.exec")
         return self.exec_results.pop(0)