fix: asSitemapCollection maybe Incompatible with prefix properties

[cscsyiku123]

🐛 The bug

import { defineCollection, defineContentConfig } from '@nuxt/content';
import { asSitemapCollection } from '@nuxtjs/sitemap/content';
export default defineContentConfig(() => {
  return {
    collections: {
      content_en: defineCollection(
        asSitemapCollection({
          type: 'page',
          source: {
            include: 'en/**',
            prefix: '',   //note
          },
        }),
     content_zh: defineCollection(
        asSitemapCollection({
          type: 'page',
          source: {
            include: 'zh/**',
            prefix: '',   //note
          },
        }),
      ),})，

In this example, when prefix is ​​set to '', zh sitemap is missing content, and when prefix is ​​not set or 'zh' sitemap is normal，this is known issue or not ?

🛠️ To reproduce

If it is not a known issue

🌈 Expected behavior

When the prefix is ", the site map still has the correct content

ℹ️ Additional context

No response