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