microversion 3.1 new fields 'visibility' and 'protected' are returned in older API microversion also

[Ghanshyam Mann]

As per api-ref these two fields 'visibility' and 'protected' were added newly in API request and response in microversion 3.1

- https://docs.openstack.org/api-ref/block-storage/v3/index.html?expanded=upload-volume-to-image-detail#volume-actions-volumes-action

But while requesting the API even with older version <3.1, these two new fields are also returned in API response. Means these new fields are always returned not only >3.1 microversion.

While checking the history, in code it was added in request with microversion protection but in response it was not protected by microversion
- https://review.opendev.org/#/c/230617/40/cinder/volume/api.py

So api-ref and what actually API behave is not same.

This is found while adding the volume API response schema in Tempest which start doing the strict validation for interop certification.

- https://review.opendev.org/#/c/616783/14/tempest/lib/api_schema/response/volume/volumes.py@244