input: Write a python function to perform a linear search in a list.
  assert linear_search([10, 20, 30, 40, 50], 20) == True
  assert linear_search([10, 20, 30, 40, 50], 60) == False
  assert linear_search([1, 2, 3, 4, 5], 3) == True
  assert linear_search([1, 2, 3, 4, 5], 6) == False
output: def linear_search(lst, target):
      for item in lst:
          if item == target:
              return True
      return False