input: Write a python function to validate credentials using a predefined dictionary.
  assert validate_credentials("testuser", "test123", creds) == True
  assert validate_credentials("testuser", "wrongpass", creds) == False
  assert validate_credentials("wronguser", "test123", creds) == False
output: def validate_credentials(username, password, creds):
      return creds.get(username) == password
  
  creds = {"testuser": "test123"}