beam_PostCommit_XVR_Dataflow flaky: Expand method not found

https://ci-beam.apache.org/job/beam_PostCommit_XVR_Dataflow/751/testReport/junit/apache_beam.transforms.validate_runner_xlang_test/ValidateRunnerXlangTest/test_combine_per_key/ et al.

Python apache_beam.transforms.validate_runner_xlang_test.ValidateRunnerXlangTest failing with error:

<_InactiveRpcError of RPC that terminated with: status = StatusCode.UNIMPLEMENTED details = "Method not found: org.apache.beam.model.expansion.v1.ExpansionService/Expand" debug_error_string = "{"created":"@1621426384.050456392","description":"Error received from peer ipv4:127.0.0.1:18091","file":"src/core/lib/surface/call.cc","file_line":1067,"grpc_message":"Method not found: org.apache.beam.model.expansion.v1.ExpansionService/Expand","grpc_status":12}" >