Fix failing test api.test_setting.test_positive_update_login_page_footer_text[login_text]

[JacobCallahan]

tests.foreman.api.test_setting.test_positive_update_login_page_footer_text[login_text] is failing in 6.9

Error message: 2021-05-06 01:07:58 - nailgun.client - WARNING - Received HTTP 422 response: { "error": {"message":"No setting value provided."} }