fix(expr): align timestamp(tz)'s output format with pg's

[KeXiangWang]

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What's changed and what's your intention?

Before:

SELECT make_timestamp(-1973, 07, 15, 08, 15, 55.33);
----
-1972-07-15 08:15:55.330

After this PR:

SELECT make_timestamp(-1973, 07, 15, 08, 15, 55.33);
----
1973-07-15 08:15:55.330 BC

Followup for #14827 (comment)

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[stdrc]

LGTM