Don't include git reference in remote.PushContext

[carsonoid]

Right now, non fast-forward errors during remote pushes create a new error which includes the git reference :

go-git/remote.go

Line 793 in d6c4b11

return fmt.Errorf("non-fast-forward update: %s", cmd.Name.String())

worktree.go has a dedicated ErrNonFastForwardUpdate error which should be used instead.

The main issue is that these two bits of code work differently:

err := w.PullContext(ctx, options) // might return a git.ErrNonFastForwardUpdate
if err != nil && err == git.ErrNonFastForwardUpdate { 
  // this code might get  executed
}


err := r.PushContext(ctx, options) // might return result of fmt.Errorf("non-fast-forward update: %s", cmd.Name.String())
if err != nil && err == git.ErrNonFastForwardUpdate { 
  // this code can never get executed
}