[php-src] PR #24608: Fix GH-24606: mbstring.http_input lost after default_charset is restored

Pull Request: https://github.com/php/php-src/pull/24608 Author: lazerg PHP_RSHUTDOWN_FUNCTION(mbstring) reset http_input_set before the INI values modified during the request get restored. Restoring default_charset then calls the encoding changed hook, which saw the flag as unset and replaced the configured mbstring.http_input list with default_charset, so later requests in the same process lost it. Only the INI handler writes http_input_set (unlike the other two flags, which mb_internal_encoding() and mb_http_output() also set), and that handler already runs again on restore when mbstring.http_input itself was changed, so the reset is not needed. Fixes #24606