CI performance improvements
CI performance improvements

Enable `bundler-cache` - ref: https://github.com/ruby/setup-ruby#caching-bundle-install-automatically
Use `MAKE` env var to improve building native extensions on MRI - ref: https://build.betterup.com/one-weird-trick-that-will-speed-up-your-bundle-install/

sferik/rails_admin,sferik/rails_admin,sferik/rails_admin