test: actually pass TZ from the running script

[aslushnikov]

The jest.config.js force-defines timezone to UTC; however, the
date tests run a matrix to set timezone to different values:

gutenberg/bin/unit-test-date.sh

Line 17 in a7fcec7

TZ=$timezone LANG=$locale \

This patch makes sure that the date tests actually test in different
timezones.

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[aslushnikov]

@Mamaduka I assume date tests want to exercise different timezones, but jest config was forcing everything in UTC.

[Mamaduka]

I'm not very familiar with this area, but I agree that these two parts contradict each other.

It looks like a change was introduced via #70578. cc @ciampo, @chihsuan

[ciampo]

Yup, if I remember correctly, we were setting the time zone to UTC in order to allow DateCalendar (and related components) tests to run reliably on every machine, instead of using local time.