input: Write a Python function to update a user's name in the database.
  assert update_user_name(1, 'Alice') == {'message': 'User updated'}
  assert update_user_name(2, 'Bob') == {'message': 'User updated'}
  assert update_user_name(3, 'Charlie') == {'message': 'User updated'}
output: def update_user_name(user_id, new_name):
      # Assuming we have a simple in-memory database for demonstration purposes
      database = {
          1: {'name': 'John'},
          2: {'name': 'Jane'},
          3: {'name': 'Doe'}
      }
      
      # Update the user's name if the user exists in the database
      if user_id in database:
          database[user_id]['name'] = new_name
          return {'message': 'User updated'}
      else:
          return {'message': 'User not found'}