input: Write a function to encrypt a message using a key in Python. The function should take two parameters, the message and the key, and return the encrypted message as a string. The encryption should be done by adding the ASCII value of each character in the message to the ASCII value of the first character of the key.
  assert encrypt("Hello world!", "secret")=="Zwzff███üóü"
  assert encrypt("Python", "key")=="U}srvn"
  assert encrypt("Data", "pass")=="?????"
  assert encrypt("Password", "123")=="Startrfv"
  assert encrypt("", "empty")==""
output: def encrypt(message, key):
      encrypted_message = ""
      key_char = ord(key[0])
      for char in message:
          encrypted_message += chr(ord(char) + key_char)
      return encrypted_message