input: Write a python function to calculate the sum of the digits in a VAT number (excluding the last check digit).
  assert sum_vat_digits("DE1905303456") == 24
  assert sum_vat_digits("FR1234567890") == 45
  assert sum_vat_digits("ES9876543210") == 45
output: def sum_vat_digits(vat_number):
      return sum(int(digit) for digit in vat_number[:-1] if digit.isdigit())