Hard-coded default branch

[bbusse]

Fails when e.g. 'main' is the default branch

[bbusse]

With go-git there currently is no way to get the default branch: go-git/go-git#510

[bbusse]

What's actually wanted is not the 'default branch' but the currently checked out HEAD I think. Maybe with something like: master...bbusse:matcha:use-current-head