bug#63857: importer fails to find “main” branch on github

[Ricardo Wurmus]

This fails:

   ./pre-inst-env guix import cran -a git -r 
https://github.com/zdebruine/singlet

With this error:

--8<---------------cut here---------------start------------->8---
Backtrace:
In guix/ui.scm:
   1374:6 19 (guix-import-cran . _)
In ice-9/boot-9.scm:
  1752:10 18 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
In guix/scripts/import/cran.scm:
   121:31 17 (_)
In guix/import/utils.scm:
   647:27 16 (recursive-import _ #:repo->guix-package _ #:guix-name _ #:version 
_ . _)
   639:33 15 (lookup-node "https://github.com/zdebruine/singlet"; #f)
In guix/memoization.scm:
     98:0 14 (mproc "https://github.com/zdebruine/singlet"; #:version #f #:repo 
git #:repo->guix-package #<procedure mproc args> #:guix-name …)
In unknown file:
          13 (_ #<procedure 7f75548c7760 at guix/memoization.scm:179:32 ()> 
#<procedure list _> (this is nothing))
In guix/import/cran.scm:
   748:24 12 (_ "https://github.com/zdebruine/singlet"; #:repo _ #:version _ 
#:license-prefix _ #:fetch-description _ #:download-source _)
   320:25 11 (fetch-description _ "https://github.com/zdebruine/singlet"; _)
In guix/memoization.scm:
     98:0 10 (mproc "https://github.com/zdebruine/singlet"; #:method git)
In unknown file:
           9 (_ #<procedure 7f75548c76c0 at guix/memoization.scm:179:32 ()> 
#<procedure list _> (this is nothing))
In ice-9/boot-9.scm:
  1752:10  8 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
In guix/store.scm:
   659:37  7 (thunk)
In guix/git.scm:
    562:8  6 (latest-repository-commit #<store-connection 256.99 7f75534a4820> 
"https://github.com/zdebruine/singlet"; #:recursive? _ # _ # _ …)
    291:4  5 (update-cached-checkout _ #:ref _ #:recursive? _ #:check-out? _ 
#:starting-commit _ #:log-port _ #:cache-directory _)
   241:18  4 (resolve _)
In git/reference.scm:
     60:8  3 (_ _ _)
In git/bindings.scm:
     77:2  2 (raise-git-error _)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Git error: reference 'refs/remotes/origin/HEAD' not found
--8<---------------cut here---------------end--------------->8---

The default branch of this repository is called “main”.

-- 
Ricardo