fix: use ExperimentalConfigWithLegacy for appDir

Author: taty2010

packages/runtime/src/index.ts

@@ -31,7 +31,7 @@ import {
   getSSRLambdas,
 } from './helpers/functions'
 import { generateRedirects, generateStaticRedirects } from './helpers/redirects'
-import { shouldSkip, isNextAuthInstalled, getCustomImageResponseHeaders, getRemotePatterns } from './helpers/utils'
+import { shouldSkip, isNextAuthInstalled, getCustomImageResponseHeaders, getRemotePatterns, ExperimentalConfigWithLegacy } from './helpers/utils'
 import {
   verifyNetlifyBuildVersion,
   checkNextSiteHasBuilt,
@@ -248,7 +248,7 @@ const plugin: NetlifyPlugin = {
     await checkZipSize(join(FUNCTIONS_DIST, `${ODB_FUNCTION_NAME}.zip`))
     const nextConfig = await getNextConfig({ publish, failBuild })
 
-    const { basePath, appDir, experimental } = nextConfig
+    const { basePath, appDir, experimental } : {basePath: string, appDir?: string, experimental: ExperimentalConfigWithLegacy} = nextConfig
 
     generateCustomHeaders(nextConfig, headers)