hopefully fix tests

Author: Conduitry

packages/kit/test/apps/basics/src/hooks.server.js

@@ -57,7 +57,7 @@ export const handle = sequence(
 		return resolve(event);
 	},
 	({ event, resolve }) => {
-		if (event.request.headers.has('user-agent') === !!event.isSyntheticRequest) {
+		if (!!event.request.headers.get('x-this-is-a-synthetic-request') !== event.isSyntheticRequest) {
 			throw new Error('Synthetic requests should have isSyntheticRequest set to true');
 		}
 		return resolve(event);
@@ -138,5 +138,7 @@ export async function handleFetch({ request, fetch }) {
 		);
 	}
 
+	request.headers.set('x-this-is-a-synthetic-request', 'true');
+
 	return fetch(request);
 }