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](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

web_src/js/markup/tasklist.js

@@ -1,4 +1,5 @@
 import {POST} from '../modules/fetch.js';
+import {showErrorToast} from '../modules/toast.js';
 
 const preventListener = (e) => e.preventDefault();
 
@@ -54,13 +55,20 @@ export function initMarkupTasklist() {
           const editContentZone = container.querySelector('.edit-content-zone');
           const updateUrl = editContentZone.getAttribute('data-update-url');
           const context = editContentZone.getAttribute('data-context');
+          const contentVersion = editContentZone.getAttribute('data-content-version');
 
           const requestBody = new FormData();
           requestBody.append('ignore_attachments', 'true');
           requestBody.append('content', newContent);
           requestBody.append('context', context);
-          await POST(updateUrl, {data: requestBody});
-
+          requestBody.append('content_version', contentVersion);
+          const response = await POST(updateUrl, {data: requestBody});
+          const data = await response.json();
+          if (response.status === 400) {
+            showErrorToast(data.errorMessage);
+            return;
+          }
+          editContentZone.setAttribute('data-content-version', data.contentVersion);
           rawContent.textContent = newContent;
         } catch (err) {
           checkbox.checked = !checkbox.checked;