ci: set_assignees: keep deferred area label on the pr

Collect the deferred area's label when a file is matched by both a
deferred file-group and a non-deferred area. The deferral removed the
area before labels were gathered, so its area label was silently lost
even though its maintainer stayed on as a reviewer.

Signed-off-by: Sylvio Alves <sylvio.alves@espressif.com>

Author: sylvioalves

scripts/ci/set_assignees.py

@@ -766,6 +766,7 @@ def process_pr(gh, args, maintainer_file, number: int):
         if _deferred and _non_deferred:
             for _area in _deferred:
                 deferred_reviewers.update(_area.maintainers)
+                labels.update(_area.labels)
                 logger.debug(
                     "  area '%s' defers to other areas for '%s'; "
                     "maintainers %s added as reviewers only",