Fix the wrong default branch name displayed by checkout (#25777)

Related: #22743

Before:

![image](https://github.com/go-gitea/gitea/assets/89133723/3cec886c-589c-41a8-86af-a08b62b8adef)

After:

![image](https://github.com/go-gitea/gitea/assets/89133723/74ee8adf-fca7-42a0-a67a-ecaa0ba91b4a)

templates/repo/branch/list.tmpl

@@ -33,7 +33,7 @@
 								{{if and $.IsWriter (not $.Repository.IsArchived) (not .IsDeleted)}}
 									<button class="btn interact-bg show-create-branch-modal gt-p-3"
 										data-modal="#create-branch-modal"
-										data-branch-from="{{$.DefaultBranchBranch}}"
+										data-branch-from="{{$.DefaultBranchBranch.DBBranch.Name}}"
 										data-branch-from-urlcomponent="{{PathEscapeSegments $.DefaultBranchBranch.DBBranch.Name}}"
 										data-tooltip-content="{{$.locale.Tr "repo.branch.new_branch_from" ($.DefaultBranchBranch.DBBranch.Name)}}"
 									>