Fix sync fork for consistency (#33147) (#33192)

Backport #33147 by changchaishi

Fixes #33145

An integration test could be added.

---------

Co-authored-by: Chai-Shi <changchaishi@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/structs/repo_branch.go

@@ -133,3 +133,11 @@ type EditBranchProtectionOption struct {
 type UpdateBranchProtectionPriories struct {
 	IDs []int64 `json:"ids"`
 }
+
+type MergeUpstreamRequest struct {
+	Branch string `json:"branch"`
+}
+
+type MergeUpstreamResponse struct {
+	MergeStyle string `json:"merge_type"`
+}