Fix 'sequence' lookup shortcut syntax and documentation (#22989)

* fix 'sequence' lookup shortcut syntax and documentation

* Update playbooks_loops.rst

Minor edits for grammar and clarity.

* Update playbooks_loops.rst

Another tweak for clarity.

lib/ansible/plugins/lookup/sequence.py

@@ -142,6 +142,8 @@ class LookupModule(LookupBase):
         if format is not None:
             self.format = format
 
+        return True
+
     def sanity_check(self):
         if self.count is None and self.end is None:
             raise AnsibleError( "must specify count or end in with_sequence")