[mjsunit] Fix intl test when LC_MESSAGES is set

This test regularly fails due to my local language setting.

Change-Id: Ic4719ffbe49a8fc9d38d75b05b52ac550315a405
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3114138
Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76448}

test/intl/regress-7770.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Environment Variables: TZ=Indian/Kerguelen LANG=uk
+// Environment Variables: TZ=Indian/Kerguelen LANG=uk LC_MESSAGES=uk
 assertEquals(
   "Fri Feb 01 2019 00:00:00 GMT+0500 (за часом на Французьких Південних і Антарктичних територіях)",
   new Date(2019, 1,1).toString());