Make our worker code backward compatible with protobuf<3.8.0

[Hazhzeng]

Description

Fixes the rest of the dispatcher not found issue.
Azure Functions Python Worker is using a Protobuf version of 3.12
Customer could break our worker code by brining a Protobuf package < 3.8.0
Issue Protobuf < 3.8.0: protocolbuffers/protobuf#6028
Fix released Protobuf >= 3.8.0: protocolbuffers/protobuf@0de6577

We should use the backward compatible syntax in worker RpcLogCategory.

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