Docs test fix, wait for shards active.

(a restore needs to be complete, which happens in the background and
by default the ccr put follow api doesn't wait for this)

(this was a recent change and the pr that added this docs test,
did not include this change)

Relates to #37917

docs/reference/ccr/apis/follow-request-body.asciidoc

@@ -51,7 +51,7 @@
 
 [source,js]
 --------------------------------------------------
-PUT /follower_index/_ccr/follow
+PUT /follower_index/_ccr/follow?wait_for_active_shards=1
 {
   "remote_cluster" : "remote_cluster",
   "leader_index" : "leader_index"