Bug#1125316: Simple fix

[Santiago Vila]

> * I can't clone the repo to begin with:
> 
> git clone git at salsa.debian.org:science-team/open-coarrays 
> Cloning into 'open-coarrays'...
> remote: Enumerating objects: 2381, done.
> remote: Counting objects: 100% (132/132), done.
> remote: Compressing objects: 100% (129/129), done.
> remote: Total 2381 (delta 59), reused 0 (delta 0), pack-reused 2249 (from 1)
> Receiving objects: 100% (2381/2381), 913.92 KiB | 1.21 MiB/s, done.
> Resolving deltas: 100% (1549/1549), done.
> warning: remote HEAD refers to nonexistent ref, unable to checkout

Note: I've just fixed this in the salsa.debian.org web interface by
doing this:

- Set default branch to something else other than debian/latest.
- Set default branch to debian/latest again.

Thanks.