[php-src] PR #23396: ext/sodium: Fix parameter name in the length-mismatch errors

Pull Request: https://github.com/php/php-src/pull/23396 Author: lacatoire The length-mismatch errors of sodium_add(), sodium_memcmp() and sodium_compare() refer to $string_2, which does not exist. All three functions declare $string2. The Argument #1 ($string1) part is generated from the arginfo and was already correct; only the hardcoded cross-reference to the second argument was stale. The added test triggers the mismatch on all three functions and lists sodium_add()'s parameter names through Reflection, so a later rename that forgets these messages fails the test.