The username format should be stricter

[wolfogre]

Description

The current username format check is

Username should contain only alphanumeric, dash ('-'), underscore ('_') and dot ('.') characters.

But I think it should be stricter, maybe

Username should contain only alphanumeric, dash ('-'), underscore ('_') and dot ('.') characters, and cannot begin or end with non-alphanumeric, consecutive non-alphanumerics are also not allowed.

What GitHub does:

Username may only contain alphanumeric characters or single hyphens, and cannot begin or end with a hyphen.

You might think this is a suggestion, not a Bug Report, so let me show you the bug.

1. Create a user named test..test;
2. Create a repo with default README.md.
3. Edit the file online and click "Commit Changes", not "Create a new branch".

I also think we can find the cause and fix the bug, but why not restrict the username format to avoid it？

Gitea Version

main@9b3e2c545

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

No response

Screenshots

No response

Git Version

No response

Operating System

No response

How are you running Gitea?

Binary file.

Database

PostgreSQL

[wxiaoguang]

There are a lot of (incorrect) checks

(Just FYI) See #20136 (comment)