Fix picker demo safe area layout (#22244)

examples/flutter_gallery/lib/demo/cupertino/cupertino_picker_demo.dart

@@ -75,6 +75,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
   Widget _buildBottomPicker(Widget picker) {
     return Container(
       height: _kPickerSheetHeight,
+      padding: const EdgeInsets.only(top: 8.0),
       color: CupertinoColors.white,
       child: DefaultTextStyle(
         style: const TextStyle(
@@ -85,6 +86,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
           // Blocks taps from propagating to the modal sheet and popping.
           onTap: () {},
           child: SafeArea(
+            top: false,
             child: picker,
           ),
         ),