bug#55618: Allow patching from mummi issues

[Nicolas Graves via Bug reports for GNU Guix <bug-guix@gnu.org>]

Hi !

I was tring to fix a local build using an online patch on mummi, this
way :

(define-public my-emacs-list-utils
  (package
    (inherit emacs-list-utils)
    (name "my-emacs-list-utils")
    (version "0.4.6")
    (source
     (origin
       (method git-fetch)
       (uri (git-reference
             (url "https://github.com/rolandwalker/list-utils")
             (commit (string-append "v" version))))
       (file-name (git-file-name name version))
       (sha256
        (base32 "07hbz2md52ccy95gv4d5n6szrfmpfqf3w4kwqdg2cf54c7kgf7hw"))
       (patches
        (list
         (origin
            (method url-fetch)
            (uri "https://issues.guix.gnu.org/issue/55498/attachment/0")
            (sha256
             (base32
              "1ysjb23g21m0jhkn63hq56snjd6skd9pl58c365g519q03hq5s87")))))))))

As it is a quick and convenient way to apply someone's work while the
patch is not upstream, I expected it to work, but it failed with the
following error during download:

Starting download of /gnu/store/v91i1m61skr42136vnxhzm4gzyidp11y-0
From https://issues.guix.gnu.org/issue/55498/attachment/0...
Bad media-type header component: text

I don't now if the fix should come from mummi's or guix's side, but I
found it a relevant way to quickly test an existing patch for one's
needs.

Thanks if you can enable this type of patches, or get alternatives if
there are. Also thanks for all the work on guix, it's amazing.

Nicolas Graves