bug#58182: 29.0.50; rename-visited-file: Selecting a directory almost works

[Lars Ingebrigtsen]

miha@kamnitnik.top writes:

> Visit an existing file and type
>
> M-x rename-visited-file RET /path/to/existing/directory/ending/with/slash/ RET
>
> and notice that the command half succeeds.
>
> The file is successfully copied to the target directory, because
> 'rename-file' handles directories. 'set-visited-file-name' doesn't
> handle directories and signals an error.

I've now fixed this in Emacs 29.