input: Write a python function to filter numbers greater than or equal to a given threshold.
  assert filter_numbers([2, 8, 10, 13, 15], 10) == [10, 13, 15]
  assert filter_numbers([1, 5, 7, 9, 11], 6) == [7, 9, 11]
  assert filter_numbers([3, 4, 5, 6, 7], 5) == [5, 6, 7]
output: def filter_numbers(numbers, threshold):
      return [num for num in numbers if num >= threshold]