[mrbtest] assert_equal(expect, actual) order fix

Follow up of #1420

This is fixing the assert_equal order of the following gems:
  - mruby-enum-ext
  - mruby-hash-ext
  - mruby-numeric-ext
  - mruby-object-ext
  - mruby-proc-ext
  - mruby-range-ext
  - mruby-string-ext
  - mruby-symbol-ext
  - mruby-toplevel-ext
  - mruby-objectspace-ext

This should finish the request in #1420.