input: Write a python function to concatenate two strings with a hyphen in between.
  assert concatenate_strings("Hello", "World") == "Hello-World"
  assert concatenate_strings("Good", "Morning") == "Good-Morning"
  assert concatenate_strings("Python", "Programming") == "Python-Programming"
output: def concatenate_strings(str1, str2):
      return f"{str1}-{str2}"