app-next: replace usage of collectLegacyRoutes

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/app-next/src/App.tsx

@@ -33,7 +33,7 @@ import {
 } from '@backstage/frontend-plugin-api';
 import techdocsPlugin from '@backstage/plugin-techdocs/alpha';
 import { homePage } from './HomePage';
-import { collectLegacyRoutes } from '@backstage/core-compat-api';
+import { convertLegacyApp } from '@backstage/core-compat-api';
 import { FlatRoutes } from '@backstage/core-app-api';
 import { Route } from 'react-router';
 import { CatalogImportPage } from '@backstage/plugin-catalog-import';
@@ -109,7 +109,7 @@ const scmIntegrationApi = createApiExtension({
   }),
 });
 
-const collectedLegacyPlugins = collectLegacyRoutes(
+const collectedLegacyPlugins = convertLegacyApp(
   <FlatRoutes>
     <Route path="/catalog-import" element={<CatalogImportPage />} />
   </FlatRoutes>,