Fix import and integrate group label

In our async retrospective issues, we noticed that the list of issues that slipped was empty even though it should have listed issues. As an example: https://gitlab.com/gl-retrospectives/manage-stage/import-and-integrate/-/issues/17#issues-that-slipped

The link redirects to https://gitlab.com/groups/gitlab-org/-/issues?label_name%5B%5D=group%3A%3Aimport%2520and%2520integrate&label_name%5B%5D=missed%3A16.11 whereas it should redirect to https://gitlab.com/groups/gitlab-org/-/issues/?sort=created_date&state=opened&label_name%5B%5D=missed%3A16.11&label_name%5B%5D=group%3A%3Aimport%20and%20integrate&first_page_size=20

Note the wrongly escaped group label.

This MR fixes the group label for groupimport and integrate