Release protocol/pubsub/v2.3.1
Correcting sub-modules to use latest release. See, https://github.com/cloudevents/sdk-go/releases/tag/v2.3.0
Correcting sub-modules to use latest release. See, https://github.com/cloudevents/sdk-go/releases/tag/v2.3.0