input: Write a python function to find the sum of even numbers in a given range.
  assert sum_even_numbers(1, 10) == 30
  assert sum_even_numbers(5, 15) == 50
  assert sum_even_numbers(2, 8) == 20
output: def sum_even_numbers(start, end):
      return sum(number for number in range(start, end + 1) if number % 2 == 0)