input: Write a python function to search for a target value in a list using linear search.
  assert search([1, 2, 3, 4, 5], 3) == 2
  assert search([10, 20, 30, 40, 50], 40) == 3
  assert search([10, 20, 30, 40, 50], 60) == -1
output: def search(lst, target):
      for i in range(len(lst)):
          if lst[i] == target:
              return i
      return -1