[BEAM-8223] Fix version number in gradle.properties for 2.16 release

[markflyhigh]

We should not include -SNAPSHOOT and .dev in version number for our release. This is a manul fix to 2.16.0 release branch. We should also fix the release automation script in the future.

+cc: @Hannah-Jiang

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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	---		---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[markflyhigh]

+R: @yifanzou @lukecwik

[Hannah-Jiang]

What is impact of this change?
I agree that we need to make the version consistent. We wanted to tackle it later, not as part of 2.16, so I added a new variable(python_sdk_version). If you confirmed all the impact of this change, I am OK with this change.

[markflyhigh]

Synced with Hannah offline. It's not about consistent naming between java's version and python's python_sdk_version. The problem this PR trying to fix is that we should not use dev version number in our release.

Test failure comes from Dataflow service side. I'll go ahead and merge it.