actions: west/devicetree: exclude python 3.6 on windows

This version of python is not available anymore. Excluding for now to
unblock CI.

Fixes: #49139

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
(cherry picked from commit 773242cb)