Remove jQuery AJAX from repo collaborator mode dropdown (#29371)

- Removed all jQuery AJAX calls and replaced with our fetch wrapper
- Tested the repo collaborator mode dropdown functionality and it works
as before

# Demo using `fetch` instead of jQuery AJAX

![action](https://github.com/go-gitea/gitea/assets/20454870/04466629-19b2-4469-9231-38820ee13c36)

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Giteabot <teabot@gitea.io>

web_src/js/features/repo-settings.js

@@ -2,6 +2,7 @@ import $ from 'jquery';
 import {minimatch} from 'minimatch';
 import {createMonaco} from './codeeditor.js';
 import {onInputDebounce, toggleElem} from '../utils/dom.js';
+import {POST} from '../modules/fetch.js';
 
 const {appSubUrl, csrfToken} = window.config;
 
@@ -11,18 +12,19 @@ export function initRepoSettingsCollaboration() {
     const $dropdown = $(e);
     const $text = $dropdown.find('> .text');
     $dropdown.dropdown({
-      action(_text, value) {
+      async action(_text, value) {
         const lastValue = $dropdown.attr('data-last-value');
-        $.post($dropdown.attr('data-url'), {
-          _csrf: csrfToken,
-          uid: $dropdown.attr('data-uid'),
-          mode: value,
-        }).fail(() => {
+        try {
+          $dropdown.attr('data-last-value', value);
+          $dropdown.dropdown('hide');
+          const data = new FormData();
+          data.append('uid', $dropdown.attr('data-uid'));
+          data.append('mode', value);
+          await POST($dropdown.attr('data-url'), {data});
+        } catch {
           $text.text('(error)'); // prevent from misleading users when error occurs
           $dropdown.attr('data-last-value', lastValue);
-        });
-        $dropdown.attr('data-last-value', value);
-        $dropdown.dropdown('hide');
+        }
       },
       onChange(_value, text, _$choice) {
         $text.text(text); // update the text when using keyboard navigating