[examples] Fix typo in `refresh_indicator` example (#119000)

examples/api/lib/material/refresh_indicator/refresh_indicator.0.dart

@@ -43,7 +43,7 @@ class _RefreshIndicatorExampleState extends State<RefreshIndicatorExample> {
         strokeWidth: 4.0,
         onRefresh: () async {
           // Replace this delay with the code to be executed during refresh
-          // and return a Future when code finishs execution.
+          // and return a Future when code finishes execution.
           return Future<void>.delayed(const Duration(seconds: 3));
         },
         // Pull from top to show refresh indicator.