input: Write a python function to return a formatted string with a username and score.
  assert formatted_string("John", 123) == "User John has a score of 123"
  assert formatted_string("Alice", 456) == "User Alice has a score of 456"
  assert formatted_string("Bob", 789) == "User Bob has a score of 789"
output: def formatted_string(username, score):
      return f"User {username} has a score of {score}"