"Commands only ..." error when submitting comment with quick action through API (/approve, /merge)

Summary

When you submit a comment with /approve through the discussions API, you'll receive Commands only Approved the current merge request error.

Steps to reproduce

1. Go to https://gitlab.com/-/graphql-explorer

2. Submit the following query

   mutation{
     createNote(input: { noteableId: "gid://gitlab/MergeRequest/122735862", body: "/approve" }) {
       errors
       note {
         body
       }
     }
   }

3. See the error

   {
     "data": {
       "createNote": {
         "errors": [
           "Commands only Approved the current merge request."
         ],
         "note": null
       }
     }
   }

Additional notes

You can get the MR id by running the following curl command:

curl -H "Authorization: Bearer $TOKEN" 'https://gitlab.com/api/v4/projects/20486274/merge_requests/13' | jq

I can't submit the comment with quick action through the REST API, but my guess would be that it's got the same issue. This is the request that fails for me:

curl -X POST -H "Authorization: Bearer $TOKEN" --form 'body=/approve'  'https://gitlab.com/api/v4/projects/20486274/merge_requests/13/discussions' | jq

Example Project

https://gitlab.com/viktomas/test-project

What is the current bug behavior?

The MR gets approved, but the API request fails.

What is the expected correct behavior?

The API request succeeds

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com