Fix samples of ExactAssetImage (#79721)

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

@@ -1006,9 +1006,11 @@ class MemoryImage extends ImageProvider<MemoryImage> {
 ///
 /// Then, to fetch the image and associate it with scale `1.5`, use:
 ///
+/// {@tool snippet}
 /// ```dart
-/// AssetImage('icons/heart.png', scale: 1.5)
+/// const ExactAssetImage('icons/heart.png', scale: 1.5)
 /// ```
+/// {@end-tool}
 ///
 /// ## Assets in packages
 ///
@@ -1016,9 +1018,11 @@ class MemoryImage extends ImageProvider<MemoryImage> {
 /// For instance, suppose the structure above is inside a package called
 /// `my_icons`. Then to fetch the image, use:
 ///
+/// {@tool snippet}
 /// ```dart
-/// AssetImage('icons/heart.png', scale: 1.5, package: 'my_icons')
+/// const ExactAssetImage('icons/heart.png', scale: 1.5, package: 'my_icons')
 /// ```
+/// {@end-tool}
 ///
 /// Assets used by the package itself should also be fetched using the [package]
 /// argument as above.