input: Write a python function to find a target string in a list and print "Target string found" if the target is present.
  assert find_target(["dog", "cat", "bird"], "bird") == "Target string found: bird"
  assert find_target(["apple", "banana", "cherry"], "banana") == "Target string found: banana"
  assert find_target(["red", "blue", "green"], "yellow") == None
output: def find_target(lst, target):
      if target in lst:
          return f"Target string found: {target}"
      return None