[BugFix][CI] Fix unittest errors caused by incorrect ray actors management

[s5u13b]

1. Fix unittest errors cause by incorrect ray actors management
   Llumnix‘s unit test raises some errors due to incorrect ray actors management. Detached actors are not killed after some test function and therefore make other test functions raise errors. This pr adds setup_ray_env pytest fixture for ray cluster management in unit test. We can pass this fixture whenever we need to create actors(that is, use ray) in test functions.
2. Fix unit test errors caused by not adding update_instance_info callback function to the scheduler.