bug#69799: 'guix refresh curl --update' queries buggy URL

[Maxim Cournoyer]

Hello, Guix!

Consider:

--8<---------------cut here---------------start------------->8---
$ guix refresh --update curl

Starting download of /tmp/guix-file.LN8KPl
>From https://curl.se/download/download/curl-8.6.0.tar.xz...
download failed "https://curl.se/download/download/curl-8.6.0.tar.xz"; 404 "Not 
Found"

Starting download of /tmp/guix-file.LN8KPl
>From 
>https://web.archive.org/web/20240314142812/https://curl.se/download/download/curl-8.6.0.tar.xz...
download failed 
"https://web.archive.org/web/20240314142812/https://curl.se/download/download/curl-8.6.0.tar.xz";
 404 "NOT FOUND"
Trying to use Disarchive to assemble /tmp/guix-file.LN8KPl...
could not find its Disarchive specification
failed to download "/tmp/guix-file.LN8KPl" from 
"https://curl.se/download/download/curl-8.6.0.tar.xz";
guix refresh: warning: curl: version 8.6.0 could not be downloaded and 
authenticated; not updating
--8<---------------cut here---------------end--------------->8---

The URL it's attempting downloading from contains a duplicate
"/download/" part, which shouldn't be there.

-- 
Thanks,
Maxim