fix: typo on "CardShapeUtil" example name (#3998)

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### Release Notes

- Fix typo on "CardShapeUtil" name in the custom shape example
documentation.

apps/docs/content/docs/shapes.mdx

@@ -151,7 +151,7 @@ We still have work to do on the `CardShapeUtil` class, but we'll come back to it
 We pass an array of our shape utils into the [Tldraw](?) component's `shapeUtils` prop.
 
 ```tsx
-const MyCustomShapes = [MyCardShape]
+const MyCustomShapes = [CardShapeUtil]
 
 export default function () {
 	return (