📝(doc) upgrade doc for Storybook v8

The Canvas block does not handle free source code anymore, now we need
to put it in a dedicated Story.

packages/react/src/components/Modal/index.mdx

@@ -1,4 +1,4 @@
-import { Canvas, Meta, Story, Source, ArgTypes } from '@storybook/blocks';
+import { Canvas, Meta, Source, ArgTypes } from '@storybook/blocks';
 import * as Stories from './index.stories';
 import * as PreBuiltStories from './PreBuilt.stories';
 import { Modal } from './index';