use private-toke to approve merge request then return 401
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When I use a private-token to approve a merge request always return 401. As following:
```
POST https://xxx.com/api/v4/projects/project_id/merge_requests/meger_request_id/approve
```
- headers contained `PRIVATE-TOKEN`
```json
{
"message": "401 Unauthorized"
}
```
issue