[php-src] PR #24288: ext/tidy: Accept null for the $encoding of the repair functions

Pull Request: https://github.com/php/php-src/pull/24288 Author: lacatoire tidy_repair_string(), tidy_repair_file(), tidy::repairString() and tidy::repairFile() declare ?string $encoding = null but parse it with Z_PARAM_STRING, so passing null is rejected. All other tidy entry points already use Z_PARAM_STRING_OR_NULL for this parameter (628db3f3b5b). null is then handled like an omitted argument: enc_len is 0 and the encoding is not set. Before (PHP-8.4, debug build with tidy): ``` $ php -d zend.assertions=1 -r 'declare(strict_types=1); tidy_repair_string("<p>test", null, null);' Fatal error: Uncaught TypeError: tidy_repair_string(): Argument #3 ($encoding) must be of type string, null given ``` After: ``` $ sapi/cli/php run-tests.php ext/tidy Tests passed : 51 (98.1%) Tests failed : 0 ( 0.0%) ``` The new test tidy_repair_encoding_null.phpt fails without the fix (the TypeError above) and passes with it.