Use the type RefName for all the needed places and fix pull mirror sync bugs (#24634)

This PR replaces all string refName as a type `git.RefName` to make the
code more maintainable.

Fix #15367
Replaces #23070 
It also fixed a bug that tags are not sync because `git remote --prune
origin` will not remove local tags if remote removed.

We in fact should use `git fetch --prune --tags origin` but not `git
remote update origin` to do the sync.

Some answer from ChatGPT as ref.

> If the git fetch --prune --tags command is not working as expected,
there could be a few reasons why. Here are a few things to check:
> 
>Make sure that you have the latest version of Git installed on your
system. You can check the version by running git --version in your
terminal. If you have an outdated version, try updating Git and see if
that resolves the issue.
> 
>Check that your Git repository is properly configured to track the
remote repository's tags. You can check this by running git config
--get-all remote.origin.fetch and verifying that it includes
+refs/tags/*:refs/tags/*. If it does not, you can add it by running git
config --add remote.origin.fetch "+refs/tags/*:refs/tags/*".
> 
>Verify that the tags you are trying to prune actually exist on the
remote repository. You can do this by running git ls-remote --tags
origin to list all the tags on the remote repository.
> 
>Check if any local tags have been created that match the names of tags
on the remote repository. If so, these local tags may be preventing the
git fetch --prune --tags command from working properly. You can delete
local tags using the git tag -d command.

---------

Co-authored-by: delvh <dev.lh@web.de>

services/repository/branch.go

@@ -139,13 +139,14 @@ func RenameBranch(ctx context.Context, repo *repo_model.Repository, doer *user_m
 	}); err != nil {
 		return "", err
 	}
-	refID, err := gitRepo.GetRefCommitID(git.BranchPrefix + to)
+	refNameTo := git.RefNameFromBranch(to)
+	refID, err := gitRepo.GetRefCommitID(refNameTo.String())
 	if err != nil {
 		return "", err
 	}
 
-	notification.NotifyDeleteRef(ctx, doer, repo, "branch", git.BranchPrefix+from)
-	notification.NotifyCreateRef(ctx, doer, repo, "branch", git.BranchPrefix+to, refID)
+	notification.NotifyDeleteRef(ctx, doer, repo, git.RefNameFromBranch(from))
+	notification.NotifyCreateRef(ctx, doer, repo, refNameTo, refID)
 
 	return "", nil
 }
@@ -187,7 +188,7 @@ func DeleteBranch(ctx context.Context, doer *user_model.User, repo *repo_model.R
 	// Don't return error below this
 	if err := PushUpdate(
 		&repo_module.PushUpdateOptions{
-			RefFullName:  git.BranchPrefix + branchName,
+			RefFullName:  git.RefNameFromBranch(branchName),
 			OldCommitID:  commit.ID.String(),
 			NewCommitID:  git.EmptySHA,
 			PusherID:     doer.ID,