write function called list_median that takes a list and returns a new list. If the list has even numbers of elements, the new list will have two elements. If the list has odd numbers of elements,
the new list will include only one element. For example:
>>> t1 = [5, 1, 2, 3, 4]
>>> list_median(t1)
[3]
>>> t2 = [8, 3, 10, 6]
>>> list_median(t2)
[6, 8]