Fix a couple of doc typos. (#60139)

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

@@ -953,7 +953,7 @@ class DropdownButton<T> extends StatefulWidget {
   /// menu that appears when you tap the button.
   ///
   /// To use a separate text style for selected item when it's displayed within
-  /// the dropdown button,, consider using [selectedItemBuilder].
+  /// the dropdown button, consider using [selectedItemBuilder].
   ///
   /// {@tool dartpad --template=stateful_widget_scaffold}
   ///

packages/flutter/lib/src/painting/decoration_image.dart

@@ -135,7 +135,7 @@ class DecorationImage {
 
   /// Defines image pixels to be shown per logical pixels.
   ///
-  /// By default the the value of scale is 1.0. The scale for the image is
+  /// By default the value of scale is 1.0. The scale for the image is
   /// calculated by multiplying [scale] with `scale` of the given [ImageProvider].
   final double scale;