Prevent possible XSS when using jQuery (#18289)

In the case of misuse or misunderstanding from a developer whereby,
if `sel` can receive user-controlled data, jQuery `$(sel)` can lead to the
creation of a new element. Current usage is using hard-coded selectors
in the templates, but nobody prevents that from expanding to
user-controlled somehow.

web_src/js/components/RepoBranchTagDropdown.js

@@ -2,7 +2,7 @@ import Vue from 'vue';
 import {vueDelimiters} from './VueComponentLoader.js';
 
 export function initRepoBranchTagDropdown(selector) {
-  $(selector).each(function () {
+  $.find(selector).each(function () {
     const $dropdown = $(this);
     const $data = $dropdown.find('.data');
     const data = {