When creating a backup fails, the volume status is changed to None

[YuehuiLei]

After the backup service is down,use the following body to create a backup:
{
    "backup": {
        "container": null,
        "description": null,
        "name": "backup001",
        "volume_id": "64f5d2fb-d836-4063-b7e2-544d5c1ff607",
        "snapshot_id": "64h8d5fb-d096-4098-n8y9-j998sj8dh6tg5",
    }
}
Backup failure is normal. But the volume status has been changed to None, which is problematic.

When there is a "snapshot_id" field in the body, it should be the backup created based on the snapshot. The snapshot status should be changed, and the volume status should not be changed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/873862