input: Write a function to convert a list of numbers into a set.
  assert list_to_set([1, 2, 3, 4, 5, 6]) == {1, 2, 3, 4, 5, 6}
  assert list_to_set([10, 20, 30, 40]) == {10, 20, 30, 40}
  assert list_to_set([7, 8, 9, 10, 11]) == {7, 8, 9, 10, 11}
output: def list_to_set(numbers):
      return set(numbers)