Pickup API proto support for NexusHandler callbacks

[chrsmith]

What changed?

This PR updates the api-go repo to pickup the latest version of api, to bring in temporalio/api#863.

Why?

Because temporalio/api#863 includes the super-duper awesome NexusHandler-variant callback type, of course! And by committing a version of api-go with it, the server-side changes can pickup the new types.

How did you test it?

I ran make test.

Potential risks

None that I am aware of.

[chrsmith]

This is the only change created by hand. (Everything else was updating the proto/api submodule, and rerunning make.)

This is the test failure without this change:

                Error:          Not equal: 
                                expected: 7
                                actual  : 8
                Test:           TestVisitedPayloads/temporal.api.update.v1.Rejection
                Messages:       expected 7 payloads reachable from temporal.api.update.v1.Rejection, found 8
                                temporal.api.update.v1.Rejection: 51 messages visited, 8 payloads seen
                                payloads seen:
                                    1. temporal.api.update.v1.Rejection.rejected_request.input.header.fields [temporal.api.common.v1.Payload]
                                    2. temporal.api.update.v1.Rejection.rejected_request.input.args [temporal.api.common.v1.Payloads]
                                    3. temporal.api.update.v1.Rejection.rejected_request.completion_callbacks.nexus_handler.source_context [temporal.api.common.v1.Payload]
                                    4. temporal.api.update.v1.Rejection.failure.encoded_attributes [temporal.api.common.v1.Payload]
                                    5. temporal.api.update.v1.Rejection.failure.application_failure_info.details [temporal.api.common.v1.Payloads]
                                    6. temporal.api.update.v1.Rejection.failure.timeout_failure_info.last_heartbeat_details [temporal.api.common.v1.Payloads]
                                    7. temporal.api.update.v1.Rejection.failure.canceled_failure_info.details [temporal.api.common.v1.Payloads]
                                    8. temporal.api.update.v1.Rejection.failure.reset_workflow_failure_info.last_heartbeat_details [temporal.api.common.v1.Payloads]

And (8) is the newly referenced commonpb.Payload, referenced from the newly added temporal.api.update.v1.Rejection.rejected_request.completion_callbacks.nexus_handler.source_context (commonpb.Callback_NexusHandler type).