fix: also apply external-link override in VPNavBarExtra

Address review feedback from @brc-dd — the translation links in
VPNavBarExtra were still being treated as external links. Apply the
same `:external="false"` override that VPNavBarTranslations uses.

src/client/theme-default/components/VPNavBarExtra.vue

@@ -33,6 +33,7 @@ const hasExtraContent = computed(
       <template v-for="locale in localeLinks" :key="locale.link">
         <VPMenuLink
           :item="locale"
+          :external="false"
           :lang="locale.lang"
           :hreflang="locale.lang"
           rel="alternate"