input: Write a python function to perform a linear search on a list and return the index of the element if found, otherwise return -1.
  assert linear_search([1, 2, 3, 4, 5], 3) == 2
  assert linear_search([10, 20, 30, 40, 50], 25) == -1
  assert linear_search([5, 7, 9, 11, 13], 13) == 4
output: def linear_search(lst, target):
      for index, element in enumerate(lst):
          if element == target:
              return index
      return -1