License compliance 'deny' testing

Test the 'deny' functionality of Licence Compliance testing, encompassing the changes from issues

#214993 (closed) Align license compliance deny classification outcome with user expectations - Add tooltip and text copy to policy tab

#214990 (closed) Align license compliance deny classification outcome with user expectations - Prevent MR from being mergable in UI

#214992 (closed) Align license compliance deny classification outcome with user expectations - Update text copy on license policy tab

#215891 (closed) Make MR not mergeable if License Compliance has found denied licenses

#215913 (closed) Allow merge when License-Check approve denied licenses

Can be linked to License Compliance test improvements as per #219461 (closed)