Switch antelope branch to unmaintained/2023.1

Antelope transitioned to unmaintained, update
build_test_packages role to reflect.

Author: karelyatin

roles/build_openstack_packages/defaults/main.yml

@@ -69,7 +69,7 @@ cifmw_bop_change_list: []
 
 cifmw_bop_release_mapping:
   master: master
-  antelope: stable/2023.1
+  antelope: unmaintained/2023.1
 
 cifmw_bop_skipped_projects:
   - testproject