test: make sure fixture prerender non-default locale as well

Author: pieh

tests/fixtures/page-router-base-path-i18n/pages/fallback-true/[slug].js

@@ -27,15 +27,16 @@ export async function getStaticProps({ params }) {
   }
 }
 
-export const getStaticPaths = () => {
+/** @type {import('next').GetStaticPaths} */
+export const getStaticPaths = ({ locales }) => {
   return {
     paths: [
       {
         params: {
           slug: 'prerendered',
         },
       },
-    ],
+    ].flatMap((pathDescription) => locales.map((locale) => ({ ...pathDescription, locale }))),
     fallback: true,
   }
 }