src: fix v8 api deprecation

PR-URL: nodejs#35700
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>

src/node_file.cc

@@ -1944,7 +1944,7 @@ static void WriteString(const FunctionCallbackInfo<Value>& args) {
       auto ext = string->GetExternalOneByteStringResource();
       buf = const_cast<char*>(ext->data());
       len = ext->length();
-    } else if (enc == UCS2 && IsLittleEndian() && string->IsExternal()) {
+    } else if (enc == UCS2 && IsLittleEndian() && string->IsExternalTwoByte()) {
       auto ext = string->GetExternalStringResource();
       buf = reinterpret_cast<char*>(const_cast<uint16_t*>(ext->data()));
       len = ext->length() * sizeof(*ext->data());