TestPubsubSignal not signalling success w/ Dataflow Runner

The issue with FhirIOReadIT seems to be some misuse of TestPubsubSignal
[Example Job](https://pantheon.corp.google.com/dataflow/jobs/us-central1/2020-05-19_19_05_19-1057064265214622054?project=apache-beam-testing) clearly has the expected \>2000 elements added to the "waitForAnyMessage" task
but the success signal never gets published to the results topic.

Notably there are job level warnings about metric descriptors and [warnings in shuffle logs](https://pantheon.corp.google.com/logs/viewer?dateRangeEnd=2020-05-20T02:18:25.642Z&dateRangeStart=2020-05-20T02:05:21.347Z&expandAll=false&interval=CUSTOM&project=apache-beam-testing&resource=dataflow_step%2Fjob_id%2F2020-05-19_19_05_19-1057064265214622054×tamp=2020-05-20T02:57:46.187000000Z&logName=projects%2Fapache-beam-testing%2Flogs%2Fdataflow.googleapis.com%252Fshuffler&minLogLevel=0&customFacets=&limitCustomFacetWidth=true&scrollTimestamp=2020-05-20T02:15:27.999165390Z) which warns:

"Update range task returned 'invalid argument'. Assuming lost lease for work with id 5061980071068333770 (expiration time: 1589940982000, now: 1589940923590, full status: INVALID_ARGUMENT: Http(400) Bad Request). For more information, see https://cloud.google.com/dataflow/docs/guides/common-errors."

Imported from Jira [BEAM-10040](https://issues.apache.org/jira/browse/BEAM-10040). Original Jira may contain additional context.
Reported by: data-runner0.