frontend-test-utils: switch createExtensionTester render to be sync

Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: Camila Belo <camilaibs@gmail.com>
Co-authored-by: Philipp Hugenroth <philipph@spotify.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/search-react/src/alpha.test.tsx

@@ -147,7 +147,7 @@ describe('createSearchResultListItemExtension', () => {
       },
     });
 
-    await createExtensionTester(SearchPageExtension)
+    createExtensionTester(SearchPageExtension)
       .add(TechDocsSearchResultItemExtension, {
         // TODO(Rugvip): We need to make the config input type available for use here
         config: {