Default to main if there is no master branch for Stash

We are currently facing an issue when pushing dinghyfile from main in stash, it complains about not finding master branch, would be nice if it looked for main also. I have noticed github has this behaviour already.
https://github.com/armory/dinghy/blame/34e05628870ab327a372e343513d06a7ece91e30/pkg/git/stash/push.go#L65C1-L68C2