input: def encrypt_message(message: str, key: str) -> str:
      """Encrypt the given message using a key by adding the unicode value of the first character of the key to each character of the message.
      >>> encrypt_message("Hello world!", "secret")
      'Tqxx{ c{uxê!'
      """
      encrypted_msg = ""
      for char in message:
          encrypted_msg += chr(ord(char) + ord(key[0]))
      return encrypted_msg
output:     encrypted_msg = ""
      for char in message:
          encrypted_msg += chr(ord(char) + ord(key[0]))
      return encrypted_msg