Update ios_system.py (#39623)

<!--- Your description here -->
Typo in the example of `domain_search`, was `domain-search`should be `domain_search`
+label: docsite_pr

lib/ansible/modules/network/ios/ios_system.py

@@ -86,7 +86,7 @@ EXAMPLES = """
   ios_system:
     hostname: ios01
     domain_name: test.example.com
-    domain-search:
+    domain_search:
       - ansible.com
       - redhat.com
       - cisco.com