Use the correct selector to hide the checkmark of selected labels on clear (go-gitea#23224)

Regression of go-gitea#10107
(https://github.com/go-gitea/gitea/pull/10107/files#diff-a15e36f2f9c13339f7fdd38bc2887db2ff2945cb8434464318ab9105fcc846bdR460)

Fix go-gitea#22222


Before: the "clear" action couldn't remove these check marks.


![image](https://user-images.githubusercontent.com/2114189/222212998-c9f33459-b71d-4e80-8588-2935f3b7050c.png)


After: the "clear" action can remove these  check marks.


![image](https://user-images.githubusercontent.com/2114189/222213048-2be98ed0-cac0-4e27-b72c-1dd0ac2637d5.png)

Author: wxiaoguang

web_src/js/features/repo-legacy.js

@@ -232,7 +232,7 @@ export function initRepoCommentForm() {
 
       $(this).parent().find('.item').each(function () {
         $(this).removeClass('checked');
-        $(this).find('.octicon').addClass('invisible');
+        $(this).find('.octicon-check').addClass('invisible');
       });
 
       if (selector === 'select-reviewers-modify' || selector === 'select-assignees-modify') {