Fix 'to to' (#28216)

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

diff --git a/packages/flutter/lib/src/material/slider_theme.dart b/packages/flutter/lib/src/material/slider_theme.dart
index 593d750..c4e0b07 100644
--- a/packages/flutter/lib/src/material/slider_theme.dart
+++ b/packages/flutter/lib/src/material/slider_theme.dart
@@ -369,7 +369,7 @@
 
   /// The shape that will be used to draw the [Slider]'s track.
   ///
-  /// The [SliderTrackShape.getPreferredRect] method is used to to map
+  /// The [SliderTrackShape.getPreferredRect] method is used to map
   /// slider-relative gesture coordinates to the correct thumb position on the
   /// track. It is also used to horizontally position tick marks, when he slider
   /// is discrete.