tests/qemu-iotests: Restrict test 134 and 158 to the 'file' protocol

tests/qemu-iotests: Restrict test 134 and 158 to the 'file' protocol

Commit b25b387fa592 updated the iotests 134 and 158 to use the --image-opts
parameter for qemu-io with file protocol related options, but forgot to
update the _supported_proto line accordingly. So let's do that now.

Fixes: b25b387fa5 ("qcow2: convert QCow2 to use QCryptoBlock for encryption")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20240315111108.153201-6-thuth@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>