Fix typo in settings_controller.dart (#91866)

Also make the spelling ThemeMode consistent

packages/flutter_tools/templates/skeleton/lib/src/settings/settings_controller.dart.tmpl

@@ -34,10 +34,10 @@ class SettingsController with ChangeNotifier {
   Future<void> updateThemeMode(ThemeMode? newThemeMode) async {
     if (newThemeMode == null) return;
 
-    // Dot not perform any work if new and old ThemeMode are identical
+    // Do not perform any work if new and old ThemeMode are identical
     if (newThemeMode == _themeMode) return;
 
-    // Otherwise, store the new theme mode in memory
+    // Otherwise, store the new ThemeMode in memory
     _themeMode = newThemeMode;
 
     // Important! Inform listeners a change has occurred.