Given a list of numbers, return a list which contains all the even numbers in the original list, which also have even indices.
get_only_evens([1, 3, 2, 6, 4, 8]) ➞ [2, 4]
get_only_evens([0, 1, 2, 3, 4]) ➞ [0, 2, 4]
get_only_evens([1, 2, 3, 4, 5]) ➞ []
Lists start at index 0.