[Docs] Missing 404 swagger response docs for /admin/users/{username}

[lonix1]

Description

The swagger endpoint /admin/users/{username} is missing the response 404.

When the account does not exist then the API returns 404 - but that is not shown in the swagger docs.

Gitea Version

1.21.0+dev-354-g24c3bb95a

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

n/a

Screenshots

No response

Git Version

n/a

Operating System

n/a

How are you running Gitea?

n/a

Database

None

[CaiCandong]

I was able to reproduce the problem, and I'm going to propose a PR to fix swagger's documentation