getNotifications type : "achievementEarned" not worked for misskey v13

[potproject]

The misskey v13 implementation of the "achievementEarned" type returns the user as null, so when getNotifications is used, an error occurs in this code section.

null is not an object (evaluating 'u.username')

https://github.com/h3poteto/megalodon/blob/master/megalodon/src/misskey/api_client.ts#L53

API Response:

[
{
    "id":"9bbz9taaoq",
    "createdAt":"2023-02-17T10:54:14.914Z",
    "type":"achievementEarned",
    "isRead":true,
    "userId":null,
    "user":null,
    "achievement":"login3"
},
...
]

[h3poteto]

refs: #1669