Fix Tooltip.decoration comment (#147858)

Tooltip decoration's comment had the backgrounds for Brightness.dark and Brightness.light swapped.

Author: karelklic

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

@@ -273,8 +273,8 @@ class Tooltip extends StatefulWidget {
   ///
   /// The tooltip shape defaults to a rounded rectangle with a border radius of
   /// 4.0. Tooltips will also default to an opacity of 90% and with the color
-  /// [Colors.grey]\[700\] if [ThemeData.brightness] is [Brightness.dark], and
-  /// [Colors.white] if it is [Brightness.light].
+  /// [Colors.grey]\[700\] if [ThemeData.brightness] is [Brightness.light], and
+  /// [Colors.white] if it is [Brightness.dark].
   final Decoration? decoration;
 
   /// The style to use for the message of the tooltip.