[fix] update types to match changes to Vite config handling (#3662)

Author: benmccann

.changeset/rude-rockets-rescue.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] update types to match changes to Vite config handling

packages/kit/types/config.d.ts

@@ -1,7 +1,7 @@
 import { CompileOptions } from 'svelte/types/compiler/interfaces';
 import { UserConfig as ViteConfig } from 'vite';
 import { CspDirectives } from './csp';
-import { RecursiveRequired } from './helper';
+import { MaybePromise, RecursiveRequired } from './helper';
 import { HttpMethod, Logger, RouteSegment, TrailingSlash } from './internal';
 
 export interface RouteDefinition {
@@ -165,7 +165,7 @@ export interface Config {
 		};
 		target?: string;
 		trailingSlash?: TrailingSlash;
-		vite?: ViteConfig | (() => ViteConfig);
+		vite?: ViteConfig | (() => MaybePromise<ViteConfig>);
 	};
 	preprocess?: any;
 }