db test: Add missing after.close call

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

test/model/database_test.dart

@@ -137,6 +137,7 @@ void main() {
         ...accountV1.toJson(),
         'ackedPushToken': null,
       });
+      await after.close();
     });
   });
 }