DEV: Clear custom sidebar sections after each test (#17775)

Initializers are re-run before each test, so we need to clear out the list to avoid duplicates building up over multiple tests.

app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js

@@ -71,6 +71,7 @@ import {
 } from "discourse/lib/to-markdown";
 import { clearTagsHtmlCallbacks } from "discourse/lib/render-tags";
 import { clearToolbarCallbacks } from "discourse/components/d-editor";
+import { resetSidebarSection } from "discourse/lib/sidebar/custom-sections";
 
 export function currentUser() {
   return User.create(sessionFixtures["/session/current.json"].current_user);
@@ -198,6 +199,7 @@ export function testCleanup(container, app) {
   clearLegacyResolverOptions();
   clearTagsHtmlCallbacks();
   clearToolbarCallbacks();
+  resetSidebarSection();
 }
 
 export function discourseModule(name, options) {