Fix about_iteration koan

* `.inject` makes an appearance here, too late to help with Warmup03!

* Good practice on various iteration methods, and useful to add to the quiver.

* `test_each_is_a_method_on_arrays` gives an error in irb as written:
   `NoMethodError: undefined method `as_name' for main:Object`

* Correct syntax in irb is: `[].methods.include?(:each)` => `true`

* `test_each_can_use_curly_brace_blocks_too`  on line 39 does not use curly braces, strange...

[#54145683]