Use GitHub Pages site origin for setting up SSG configs

src/fixtures/sveltekit/blank.expected.js

@@ -3,6 +3,7 @@ import adapter from '@sveltejs/adapter-auto'
 
 export default {
   kit: {
+    prerender: { origin: 'https://configure-pages.github.io' },
     paths: { base: '/docs' },
     adapter: adapter()
   }

src/fixtures/sveltekit/default.expected.js

@@ -3,6 +3,7 @@ import adapter from '@sveltejs/adapter-auto'
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
   kit: {
+    prerender: { origin: 'https://configure-pages.github.io' },
     paths: { base: '/docs' },
     adapter: adapter()
   }