Ensure onmouseleave event fires in Hoverable example (#7873)

Fixes the browser-quirk-related issue described in #6520 and #7867, based on a [suggestion](https://github.com/sveltejs/svelte/issues/7867#issuecomment-1248993436) by @Prinzhorn.

Tested in the editable example area on the Svelte site: https://svelte.dev/examples/slot-props

site/content/examples/15-composition/03-slot-props/App.svelte

@@ -43,4 +43,8 @@
 		background-color: #ff3e00;
 		color: white;
 	}
-</style>
+	
+	p {
+		pointer-events: none;
+	}
+</style>