Fix async cursor close method

Author: vgvoleg

ydb_sqlalchemy/sqlalchemy/dbapi_adapter.py

@@ -105,7 +105,7 @@ def executemany(self, sql, parameters=None):
         return await_only(self._cursor.executemany(sql, parameters))
 
     def close(self):
-        return await_only(self._cursor.close())
+        return self._cursor.close()
 
     def setinputsizes(self, *args):
         pass