[BEAM-8358] Fixes the failing test issue in UTC+8 timezone

[zkauker]

The date converter converted the UTC timestamp to ZonedDateTime first and then truncated the timestamp to date. With the timestamp in the unit test, this led to the expected date + 1 day in UTC+8 timezone.

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

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[zkauker]

R: @reuvenlax
R: @iemejia
R: @JawadHyder
R: @lukecwik

[lukecwik]

Is there a way you could add a test for this?

[stale]

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[stale]

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