input: Write a function to find the common elements between two lists and return them in a new list. If there are no common elements, return an empty list.
  common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10]) == [2, 8]
  common_elements([1, 2, 3], [4, 5, 6]) == []
  common_elements([], [1, 2, 3]) == []
  common_elements([1, 2, 3], []) == []
  common_elements([1, 2, 2, 3], [2, 2, 3, 4]) == [2, 2, 3]
output: def common_elements(list1, list2):
      return [item for item in list1 if item in list2]