Fix handler listeners as a list
Fix handler listeners as a list

The listen statement on handlers should have supported a list, however
it was broken in the revision of the pub/sub feature based on the handler
revamp. This patch corrects the bug, so this works again:

- name: some handler
  ...
  listen:
  - some target
  - another target

Fixes #16378

thaim/ansible,thaim/ansible