[php-src] PR #24406: ext/iconv, ext/standard: make tests more robust on FreeBSD

Pull Request: https://github.com/php/php-src/pull/24406 Author: Sjord I ran PHP's tests on FreeBSD 15.1, and these were failing: - ext/iconv/tests/bug52211.phpt: trigger the error with an incomplete UTF-8 source sequence. Rejecting a valid but unrepresentable character is implementation-defined; FreeBSD's ASCII passes bytes through for identity conversions, while glibc rejects them. https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=296765 - ext/standard/tests/file/chmod_basic.phpt: probe which special mode bits can be set on a regular file. FreeBSD rejects the sticky bit on regular files with EFTYPE. - ext/standard/tests/file/006_variation2.phpt: apply the sticky bit only to the directory, whose semantics are portable, and update the expected file modes. - ext/standard/tests/ini_info/php_ini_loaded_file.phpt: do not forward TEST_PHP_EXTRA_ARGS for the "no ini file" case. It can contain -c, which takes precedence over -n, causing the child to load run-tests.php's temporary ini file. Also clear the stat cache before calling fileperms(), not after.