fix incorrect repo url when changed the case of ownername (#25733)

fix incorrect repo url when changed the case of ownername (#25733)

When only the case of the username changes and the new username is
consistent with the lowercase username of the old user name, update the
owner name of the repo, and keep the original logic consistent with
other conditions.

example: your username is `gitea`, lowercase username is `gitea`,repo
url is `.../gitea/{repo}`, you changed username to `Gitea` or `GiTea` or
other, but the lowercase username is still `gitea`, the repo url is
still `.../gitea/{repo}`.

this pr fixed it,keep username and repo url consistent.

Before:

![image](https://github.com/go-gitea/gitea/assets/89133723/84177296-f0ff-4176-84f1-1f9ec3f5b86f)

![image](https://github.com/go-gitea/gitea/assets/89133723/8f8f4a12-ecdd-4dec-af89-85c009b0ccfe)

After:

![image](https://github.com/go-gitea/gitea/assets/89133723/0564edb6-9467-405a-8cd4-d6f70e6f614b)

![image](https://github.com/go-gitea/gitea/assets/89133723/554ecd6e-e5a1-43bc-a46d-99e988c2ff58)