Do not run rubocop on non-CRuby (#2737)
Do not run rubocop on non-CRuby (#2737)

It does not seem useful (redundant with running it on CRuby), makes builds slower, and also sometimes makes builds fail: https://github.com/puma/puma/runs/4047984193?check_suite_focus=true
eileencodes/puma,puma/puma,eileencodes/puma,puma/puma,eileencodes/puma,eileencodes/puma,puma/puma,puma/puma