[JUJU-1537] Install latest stable lxd version for pylib integration.

[juanmanuel-tirado]

In one of the executions of the pylib integrations tests we found a message indicating that lxd 4.24/stable package is missing. Install the default lxd snap package available at the moment.

sudo snap install lxd --channel=4.24/stable
09:51:08 error: snap "lxd" is not available on 4.24/stable but is available to install
09:51:08        on the following channels:
09:51:08 
09:51:08        4.24/candidate  snap install --channel=4.24/candidate lxd
09:51:08        4.24/beta       snap install --channel=4.24/beta lxd
09:51:08        4.24/edge       snap install --channel=4.24/edge lxd
09:51:08 
09:51:08        Please be mindful pre-release channels may include features not
09:51:08        completely tested or implemented. Get more information with 'snap info
09:51:08        lxd'.