[php-src] PR #24215: Fix unpack() offset error naming a nonexistent parameter

Pull Request: https://github.com/php/php-src/pull/24215 Author: lacatoire The unpack() error for an out-of-range $offset names a parameter that does not exist. The signature is unpack(string $format, string $string, int $offset = 0), and $data was renamed to $string in 25f1c405ff. ```php try { unpack("N", "abcd", 9); } catch (ValueError $e) { echo $e->getMessage(); } ``` Before: ``` unpack(): Argument #3 ($offset) must be contained in argument #2 ($data) ``` After: ``` unpack(): Argument #3 ($offset) must be contained in argument #2 ($string) ``` unpack_offset.phpt is updated, and now also lists the parameter names through Reflection so a future rename cannot leave this message stale. The test passes.