Type false session as null

Make the typing for the session work again by telling TypeScript the
false value is actually null.

composables/session.ts

@@ -1,7 +1,7 @@
 export const useAccountSession = () => useFetch(
 	"/api/auth/session",
 	{
-		transform: (input) => input === undefined ? false : input,
+		transform: (input) => input === undefined ? false as any as null: input,
 		getCachedData(key, nuxtApp) {
 			return nuxtApp.payload.data[key];
 		},