helpers/generate_common.sh: use HEAD instead of master
The master is not default for all repositories and there are some existing repositories that migrated to the different default branch name. The git provides instead generic alias HEAD for current branch that on remote is resolved to the default branch and thus to master or what it is called in that project. The issue is that while HEAD works when we fetch we can't use it for checkout because it references the local HEAD in that case. We have to use FETCH_HEAD instead as that is the reference git gives to head fetched from the remote server.
bugfix/generate-checkout-default in 5 minutes and 19 seconds (queued for 8 seconds)7 jobs for