Generate random valid 9-digit REGON.

        :return: Valid 9-digit REGON

def regon(self) -> str:
        """Generate random valid 9-digit REGON.

        :return: Valid 9-digit REGON
        """
        regon_coeffs = (8, 9, 2, 3, 4, 5, 6, 7)
        regon_digits = [self.random.randint(0, 9) for _ in range(8)]
        sum_v = sum([nc * nd for nc, nd in
                     zip(regon_coeffs, regon_digits)])
        checksum_digit = sum_v % 11
        if checksum_digit > 9:
            checksum_digit = 0
        regon_digits.append(checksum_digit)
        return ''.join(str(d) for d in regon_digits)