[BEAM-8165] use default tag

[Hannah-Jiang]

Use default tag which is latest instead of version.

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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.

[Hannah-Jiang]

Run JavaPortabilityApi PreCommit

[Hannah-Jiang]

R: @yifanzou

[yifanzou]

The code looks good. A few questions: What would the default tag look like? Doesn't python images use the default tags?

[Hannah-Jiang]

The code looks good. A few questions: What would the default tag look like? Doesn't python images use the default tags?

Default tag is latest, which is defined here.
Python doesn't use default tag because it can read version from version.py.

[Hannah-Jiang]

Run Python PreCommit