Fix no edit history after editing issue's title and content (#30814)

Fix #30807

reuse functions in services

modules/structs/pull.go

@@ -85,7 +85,7 @@ type CreatePullRequestOption struct {
 // EditPullRequestOption options when modify pull request
 type EditPullRequestOption struct {
 	Title     string   `json:"title"`
-	Body      string   `json:"body"`
+	Body      *string  `json:"body"`
 	Base      string   `json:"base"`
 	Assignee  string   `json:"assignee"`
 	Assignees []string `json:"assignees"`