Fix <IntersectionObserver /> behaviour in tests

vite.config.ts

@@ -1,13 +1,13 @@
 import { sveltekit } from '@sveltejs/kit/vite';
-import type { UserConfig } from 'vite';
 
-const config: UserConfig = {
+export default {
 	plugins: [sveltekit()],
 	test: {
 		include: ['src/**/*.{test,spec}.{js,ts}'],
 		environment: 'jsdom',
 		globals: true,
+		// Carefully see this thread to understand the next lines and
+		// how they can impact the Svelte IntersectionObserver.
+		alias: [{ find: /^svelte$/, replacement: 'svelte/internal' }]
 	}
 };
-
-export default config;