input: Write a function to encrypt a message using a key in Python. The function should take a message and a key as input and return the encrypted message. The encryption should be done by adding the ASCII value of the first character of the key to each character in the message.
  assert encrypt("Hello world!", "secret")=="Tqxx{ y{|{~"
  assert encrypt("Good morning!", "key")=="Qqqe &qsvrmrk'"
  assert encrypt("Keep it secret!", "password")=="[mtt{!u%xìgmu{"
  assert encrypt("Python is fun!", "code")=="T{ymto+|&mx|/"
output: def encrypt(message, key):
      encrypted_message = ""
      key_value = ord(key[0])
      for char in message:
          encrypted_message += chr(ord(char) + key_value)
      return encrypted_message