_DropdownMenuState should dispose TextEditingController. (#133914)

packages/flutter/lib/src/material/dropdown_menu.dart

@@ -541,6 +541,9 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
 
   @override
   void dispose() {
+    if (widget.controller == null) {
+      _textEditingController.dispose();
+    }
     super.dispose();
   }
 

packages/flutter/test/material/dropdown_menu_theme_test.dart

@@ -100,7 +100,7 @@ void main() {
     expect(material.textStyle?.color, themeData.colorScheme.onSurface);
   });
 
-  testWidgets('ThemeData.dropdownMenuTheme overrides defaults', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('ThemeData.dropdownMenuTheme overrides defaults', (WidgetTester tester) async {
     final ThemeData theme = ThemeData(
       dropdownMenuTheme: DropdownMenuThemeData(
         textStyle: TextStyle(