docs: 'ansible_play_hosts' lists active hosts, not limited by serial (#…

…71116)

ansible_play_batch lists the currently targeted host(s) in the serial/batch, while
ansible_play_hosts lists all the hosts which will be targeted by the play.

docs/docsite/rst/reference_appendices/special_variables.rst

@@ -51,7 +51,7 @@ ansible_play_batch
     List of active hosts in the current play run limited by the serial, aka 'batch'. Failed/Unreachable hosts are not considered 'active'.
 
 ansible_play_hosts
-    The same as ansible_play_batch
+    List of hosts in the current play run, not limited by the serial. Failed/Unreachable hosts are included in this list.
 
 ansible_play_hosts_all
     List of all the hosts that were targeted by the play