[BEAM-11418][BEAM-9920] Fix Go universal runner x-lang artifact staging.

[youngoli]

When x-lang artifacts were being requested by the SDK harness, this staging code was just sending out the Go worker binary for everything, which is definitely not intended behavior. This commit fixes that and actually reads the artifact payload to get the desired artifact.

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ValidatesRunner compliance status (on master branch)

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---			---		---
Java
Python	---			---		---
XLang				---		---

Examples testing status on various runners

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---	---	---	---	---	---	---
Java	---		---	---	---	---	---
Python	---	---	---	---	---	---	---
XLang	---	---	---	---	---	---	---

Post-Commit SDK/Transform Integration Tests Status (on master branch)

Go	Java	Python

Pre-Commit Tests Status (on master branch)

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

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

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[youngoli]

R: @lostluck

[lostluck]

windmill slam approve Great find! Thanks Daniel!

[lostluck]

Run Go PostCommit