[releng] Prepare repo for CDT 11.0.1 development
Run all workflows on CDT 11 branch too
Use Ubuntu that contains GDB 10Until we are ready for GDB 12 in the testsuite, run the GHAchecks against GDB 10 by chaning base OS to Ubuntu 20.04instead of latest (which recently changed to 22.04)Worksaround #210