Added a missing dispose of an AnimationController that was causing a ticker leak. (#32843)

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

@@ -736,6 +736,7 @@ class _MonthPickerState extends State<MonthPicker> with SingleTickerProviderStat
   @override
   void dispose() {
     _timer?.cancel();
+    _chevronOpacityController?.dispose();
     _dayPickerController?.dispose();
     super.dispose();
   }