Prevent simultaneous editing of comments and issues (#31053)

fixes #22907

Tested:
- [x] issue content edit
- [x] issue content change tasklist
- [x] pull request content edit
- [x] pull request change tasklist

![issue-content-edit](https://github.com/go-gitea/gitea/assets/29250154/a0828889-fb96-4bc4-8600-da92e3205812)

(cherry picked from commit aa92b13164e84c26be91153b6022220ce0a27720)

Conflicts:
	models/issues/comment.go
	 c7a389f2b2 [FEAT] allow setting the update date on issues and comments

	options/locale/locale_en-US.ini
	 trivial context conflicts

	routers/api/v1/repo/issue_comment.go
	routers/api/v1/repo/issue_comment_attachment.go
	services/issue/comments.go
	services/issue/content.go
         user blocking is implemented differently in Forgejo

	routers/web/repo/issue.go
	 trivial difference from 6a0750177f Allow to save empty comment
         user blocking is implemented differently in Forgejo

	templates/repo/issue/view_content/conversation.tmpl
	 templates changed a lot in Forgejo but the change is
	 trivially ported

	tests/integration/issue_test.go
	 other tests were added in the same region

	web_src/js/features/repo-issue-edit.js
	 the code is still web_src/js/features/repo-legacy.js
	 trivially ported

routers/api/v1/repo/pull.go

@@ -609,8 +609,13 @@ func EditPullRequest(ctx *context.APIContext) {
 		}
 	}
 	if form.Body != nil {
-		err = issue_service.ChangeContent(ctx, issue, ctx.Doer, *form.Body)
+		err = issue_service.ChangeContent(ctx, issue, ctx.Doer, *form.Body, issue.ContentVersion)
 		if err != nil {
+			if errors.Is(err, issues_model.ErrIssueAlreadyChanged) {
+				ctx.Error(http.StatusBadRequest, "ChangeContent", err)
+				return
+			}
+
 			ctx.Error(http.StatusInternalServerError, "ChangeContent", err)
 			return
 		}