[frontend] fixup test fixtures for Rawhide
    
    ==================================== ERRORS ====================================
     ERROR at setup of TestBuildsLogic.test_add_raises_if_copr_has_unfinished_actions
    Fixture "f_db" called directly. Fixtures are not meant to be called directly,
    but are created automatically when test functions request them as parameters.
    See https://docs.pytest.org/en/latest/fixture.html for more information about fixtures, and
    
    Fixes: PR#658