Use JSON instead of Gitlab::Json

Signed-off-by: Rémy Coutable <remy@rymai.me>

keeps/helpers/groups.rb

@@ -41,7 +41,7 @@ def fetch_groups
               "Failed to get group information with response code: #{response.code} and body:\n#{response.body}"
           end
 
-          Gitlab::Json.parse(response.body)
+          JSON.parse(response.body) # rubocop:disable Gitlab:Json -- We don't rely on GitLab internal classes
         end
       end
     end