fix: prevent adding multiple x-default alternate links

Author: BobbieGoede

src/runtime/kit/head.ts

@@ -134,7 +134,7 @@ function getHreflangLinks(options: HeadContext) {
     if (!link) continue
 
     links.push(link)
-    if (options.defaultLocale && options.defaultLocale === locale.code) {
+    if (options.defaultLocale && options.defaultLocale === locale.code && links[0].hreflang !== 'x-default') {
       links.unshift(
         strictSeo
           ? { rel: 'alternate', href: link.href, hreflang: 'x-default' }