Fix checking out a different branch while pushing a branch for the first time

When pushing a branch that didn't have an upstream yet, we use the command line

  git push --set-upstream origin HEAD:branch-name

The HEAD: part of this is too unspecific; when checking out a different branch
while the push is still running, then git will set the upstream branch on the
newly checked out branch, not the branch that was being pushed. This might be
considered a bug in git; you might expect that it resolves HEAD at the beginning
of the operation, and uses the result at the end.

But we can easily work around this by explicitly supplying the real branch name
instead of HEAD.

pkg/commands/git_commands/sync.go

@@ -1,6 +1,8 @@
 package git_commands
 
 import (
+	"fmt"
+
 	"github.com/go-errors/errors"
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
@@ -20,6 +22,7 @@ func NewSyncCommands(gitCommon *GitCommon) *SyncCommands {
 type PushOpts struct {
 	Force          bool
 	ForceWithLease bool
+	CurrentBranch  string
 	UpstreamRemote string
 	UpstreamBranch string
 	SetUpstream    bool
@@ -35,7 +38,7 @@ func (self *SyncCommands) PushCmdObj(task gocui.Task, opts PushOpts) (oscommands
 		ArgIf(opts.ForceWithLease, "--force-with-lease").
 		ArgIf(opts.SetUpstream, "--set-upstream").
 		ArgIf(opts.UpstreamRemote != "", opts.UpstreamRemote).
-		ArgIf(opts.UpstreamBranch != "", "HEAD:"+opts.UpstreamBranch).
+		ArgIf(opts.UpstreamBranch != "", fmt.Sprintf("refs/heads/%s:%s", opts.CurrentBranch, opts.UpstreamBranch)).
 		ToArgv()
 
 	cmdObj := self.cmd.New(cmdArgs).PromptOnCredentialRequest(task)