input: Write a function to check if an item exists in a given list.
  assert is_item_in_list(3, [1, 2, 3, 4, 5])==True
  assert is_item_in_list(6, [1, 2, 3, 4, 5])==False
  assert is_item_in_list('a', ['a', 'b', 'c'])==True
  assert is_item_in_list('z', ['a', 'b', 'c'])==False
output: def is_item_in_list(item, lst):
      return item in lst