Special README paths can be infinitely nested

[kousu]

Description

Gitea supports loading READMEs from ./README.md but also ./README, ./README.txt, ./README.zh.md, etc, and also also ./docs/README.md, ./.github/README.md, ./.gitea/README.md.

But currently it also supports infinitely nested copies of these special subdirs, like this regex: ./({docs,.github,.gitea}/)+README.*

Eg. https://try.gitea.io/kousu/test-readme-recurse/

Gitea Version

1.20.0+dev-265-gc5cfc0855

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

No response

Screenshots

Git Version

2.24.1

Operating System

Ubuntu 22.04

How are you running Gitea?

I built mine at home.

Database

SQLite

[kousu]

This was introduced when I was responding to code review during #22177.

There is a test I added in #23185 for this, but I left commented out because I knew this was broken.