test: set LC_ALL to known good value

Set the locale to a known good value because it affects ICU's date
string formatting. Setting LC_ALL needs to happen before the first
call to `icu::Locale::getDefault()` because ICU caches the result.

Fixes: nodejs#27856

test/parallel/test-process-env-tz.js

@@ -1,5 +1,10 @@
 'use strict';
 
+// Set the locale to a known good value because it affects ICU's date string
+// formatting. Setting LC_ALL needs to happen before the first call to
+// `icu::Locale::getDefault()` because ICU caches the result.
+process.env.LC_ALL = 'C';
+
 const common = require('../common');
 const assert = require('assert');