[BEAM-11537] Fix TestPubSubSignal.waitForStart

[TheNeuralBit]

I had the subscription and topic arguments reversed in this call.

Post-Commit Tests Status (on master branch)

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

Pre-Commit Tests Status (on master branch)

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

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GitHub Actions Tests Status (on master branch)

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[TheNeuralBit]

Run Java PostCommit

[TheNeuralBit]

R: @boyuanzz

[boyuanzz]

Thanks for the quick fix! Feel free to merge it once all tests pass.

[TheNeuralBit]

Run Java PostCommit

[TheNeuralBit]

It looks like the remaining failure in FhirIOSearchIT.testFhirIOSearch[R4] is another postcommit breakage, first appeared in https://ci-beam.apache.org/job/beam_PostCommit_Java/7016/

I'm going to go ahead and merge this then triage the other test.

[TheNeuralBit]

Nevermind based on the history it looks like the testFhirIOSearch failure may be some flakiness introduced by #13516