run_level.rb - convert class var to class ivar

[nimmolo]

This @@class_var is not used outside the class, so it seems safe to convert to an ivar.

[JoeCohen]

@nimmolo: I hadn't reviewed this because of the push test failure.
I often just re-run the failing test in Github when I see a CI failure because of a system test. But Github isn't giving me that option for this failure.
Is that something you can try?
It would be nice to get your work into main.