Set timezone for karma to UTC

changelogs/unreleased/42251-explicit-timezone-for-karma.yml

+---
+title: Set timezone for karma to UTC
+merge_request: 16602
+author: Takuya Noguchi
+type: other

config/karma.config.js

@@ -18,6 +18,8 @@ webpackConfig.devtool = 'cheap-inline-source-map';
 // Karma configuration
 module.exports = function(config) {
+  process.env.TZ = 'Etc/UTC';
+
   var progressReporter = process.env.CI ? 'mocha' : 'progress';
   var karmaConfig = {