input: 
  def encrypt(message: str, key: str) -> str:
      """
      Encrypt a message using a key by adding the ASCII value of the key to each character in the message.
      The encrypted message is formed by taking each character of the message, transforming it by adding the ASCII value of the first character of the key, and then converting it back to a string.
      
      >>> encrypt("Hello world!", "secret")
      'Tqxx{¦yq}~'
      """
  
output:     encrypted_message = ""
      key_char = ord(key[0])
      for char in message:
          encrypted_message += chr(ord(char) + key_char)
      return encrypted_message