input: Write a function to encrypt a message using a key in Python. The function should take two arguments: the message to be encrypted and the encryption key. The encryption algorithm should add the Unicode value of the first character of the key to the Unicode value of each character in the message to generate the encrypted message.
  def encrypt(message, key):
      encrypted_msg = ""
      for char in message:
          encrypted_msg += chr(ord(char) + ord(key[0]))
      return encrypted_msg
  
  assert encrypt("Hello world!", "secret")=="Ts222 2t|_2|2A"
  assert encrypt("Hello", "key")=="Mn111"
  assert encrypt("Testing", "a")=="UftujoH"
  assert encrypt("", "secret")==""
  assert encrypt("Python", "z")=="Ayrgsm"
output: def encrypt(message, key):
      encrypted_msg = ""
      for char in message:
          encrypted_msg += chr(ord(char) + ord(key[0]))
      return encrypted_msg