Recent clients fail against older services due to microversion compatibility

Using release 8.3.0 or newer of the client against a Xena service fails, even when specifying an older microversion with --os-volume-api-version:

ERROR: Version 3.68 is not supported by the API. Minimum is 3.0 and maximum is 3.66. (HTTP 406)

It works with client 8.2.0 because its maximum supported version is 3.66.

This is because the cinder client makes an initial request to the root API resource without respecting the provided API version:

$ cinder --os-volume-api-version 3.28 --debug service-list
[...]
DEBUG:keystoneauth:REQ: curl -g -i -X GET https://example.com:8776/ -H "Accept: application/json" -H "OpenStack-API-Version: volume 3.68" -H "User-Agent: python-cinderclient" -H "X-Auth-Token: {SHA256}REDACTED"
DEBUG:keystoneauth:RESP: [406] content-length: 123 content-type: application/json date: Fri, 02 Dec 2022 12:27:34 GMT openstack-api-version: volume 3.68 server: Apache/2.4.41 (Ubuntu) vary: OpenStack-API-Version
DEBUG:keystoneauth:RESP BODY: {"computeFault": {"code": 406, "message": "Version 3.68 is not supported by the API. Minimum is 3.0 and maximum is 3.66."}}
DEBUG (shell:1031) Version 3.68 is not supported by the API. Minimum is 3.0 and maximum is 3.66. (HTTP 406)