test(TzDate): fix test in Australia

Probably due to implementation differences in browsers for pre-DST period (see
https://github.com/angular/angular.js/issues/5017 and especially
https://github.com/angular/angular.js/issues/5017#issuecomment-90775226 for context), some
`TzDate` tests had different behavior on different Timezones/Regions (e.g. failed in Australia,
which started to observe DST in 1971).
Since the used year (`1970`) didn't have any particular significance, this commit fixes the issue
by using a year that is more consistently handled by browsers (`2000`).

Fixes #14272

Closes #14285