[css-lists-3] Correct markup for nested lists example (#12189)

Author: manuel-za

css-lists-3/Overview.bs

@@ -1326,8 +1326,8 @@ The Implicit ''list-item'' Counter</h3>
 								<li>Third third-level item in reversed list
 								<li>Fourth third-level item in reversed list
 							</ol>
+						<li>Third second-level item, list start=3
 					</ol>
-				<li>Third second-level item, list start=3
 				<li>Third top-level item
 			</ol>
 		</xmp>