Fix Doxygen issues

[embhorn]

• Fix issues in documentation generation:

  
  Generating docs for compoun/var/lib/jenkins/workspace/wolfSSL/nightly-docs-job-v2/wolfMQTT/wolfmqtt/wolfmqtt/mqtt_client.h:256: warning: documented empty return type of MqttClient_DeInit

/var/lib/jenkins/workspace/wolfSSL/nightly-docs-job-v2/wolfMQTT/wolfmqtt/wolfmqtt/mqtt_client.h:369: warning: The following parameter of MqttClient_Publish_WriteOnly(MqttClient client, MqttPublish publish, MqttPublishCb pubCb) is not documented: parameter 'pubCb'

* Fix MacOS workflow
* Fix Zephyr workflow build errors