Use querySelector over alternative DOM methods (#31280)

As per
https://github.com/go-gitea/gitea/pull/30115#discussion_r1626060164,
prefer `querySelector` by enabling
[`unicorn/prefer-query-selector`](https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/prefer-query-selector.md)
and autofixing all except 10 issues.

According to
[this](https://old.reddit.com/r/learnjavascript/comments/i0f5o8/performance_of_getelementbyid_vs_queryselector/),
querySelector may be faster as well, so it's a win-win.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

web_src/js/features/repo-editor.js

@@ -112,7 +112,7 @@ export function initRepoEditor() {
 
     // Using events from https://github.com/codedance/jquery.AreYouSure#advanced-usage
     // to enable or disable the commit button
-    const commitButton = document.getElementById('commit-button');
+    const commitButton = document.querySelector('#commit-button');
     const $editForm = $('.ui.edit.form');
     const dirtyFileClass = 'dirty-file';