docs: remove typescript syntax from javascript example (#3412)

Author: ausir0726

docs/content/docs/02.guide/06.seo.md

@@ -243,7 +243,7 @@ useHead({
     const i18nHead = useLocaleHead({ seo: { canonicalQueries: ['foo'] } })
     useHead(() => ({
       htmlAttrs: {
-        lang: i18nHead.value.htmlAttrs!.lang
+        lang: i18nHead.value.htmlAttrs.lang
       },
       link: [...(i18nHead.value.link || [])],
       meta: [...(i18nHead.value.meta || [])]