Locked time zone for tests

[raysarebest]

Phabricator: N/A

Notes

testEditMilestoneHundredOnUserTalkPage() in the default test suite would fail if the test system was set to a time zone far enough east. This is due to the fact that it compares against the string literal "7/16/21", but uses a date formatter that depends on the current system calendar/time zone/etc

This PR addresses this issue by locking the time zone on the test system to America/New_York, thereby eliminating the system time zone as a dependency of the tests

Test Steps

1. Set the system the tests will be run upon to Europe/Amsterdam (or other Central European time zone)
2. Run the default Wikipedia test suite
3. Observe that all the tests (including testEditMilestoneHundredOnUserTalkPage()) pass