Update example to match docs

In the documentation for the "enabled" parameter, two choices are listed "true" or "false".  The example below uses "yes." I understand that both work, but IMO it's a bit more clear if the example matches the definition.

lib/ansible/modules/service.py

@@ -140,7 +140,7 @@ EXAMPLES = r'''
 - name: Enable service httpd, and not touch the state
   ansible.builtin.service:
     name: httpd
-    enabled: yes
+    enabled: true
 
 - name: Start service foo, based on running process /usr/bin/foo
   ansible.builtin.service: