Fix incompatibility with existing database migrator after SQLAlchemy 2.0.

bemani/data/data.py

@@ -135,7 +135,7 @@ class Data:
         # See if the DB was already created
         try:
             cursor = self.__session.execute(text("SELECT COUNT(version_num) AS count FROM alembic_version"))
-            return cursor.fetchone()["count"] == 1
+            return cursor.mappings().fetchone()["count"] == 1
         except ProgrammingError:
             return False