tests: adapt waiting for index search to whoosh write lock (#32031)

tests/test_search.py

@@ -396,6 +396,7 @@ def test_manager_waiting_index_message(app, admin_user):
     resp = resp.form.submit().follow()
     assert 'Content indexing has been scheduled' in resp.text
 
+    os.mkdir(connections['default'].get_backend().path)
     call_command('update_index')
     resp = app.get('/manage/pages/%s/' % page.id)
     assert 'Content indexing has been scheduled' not in resp.text