Set timezone to GMT in Jest config

jest.config.js

@@ -2,6 +2,10 @@ const IS_EE = require('./config/helpers/is_ee_env');
 
 const reporters = ['default'];
 
+// To have consistent date time parsing both in local and CI environments we set
+// the timezone of the Node process. https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27738
+process.env.TZ = 'GMT';
+
 if (process.env.CI) {
   reporters.push([
     'jest-junit',