[php-src] PR #24201: Bug: Memory leak of the last response headers after a nested HTTP request

Pull Request: https://github.com/php/php-src/pull/24201 Author: EdmondDantes php_stream_url_wrap_http() releases BG(last_http_headers) before the request and copies the new headers over it after the request. A request made from the notification callback of a running one stores its own headers there in between, and the outer copy overwrote that array without releasing it. Reproduction (debug build, no extensions beyond pcntl and posix for the test server): ```php $ctx = stream_context_create([], ['notification' => function ($code) use (&$nested, $uri) { if ($code === STREAM_NOTIFY_MIME_TYPE_IS && !$nested) { $nested = true; file_get_contents($uri); } }]); file_get_contents($uri, false, $ctx); ``` Expected: no leak. Actual: === Total 4 memory leaks detected === (the nested request's header array). The fix releases the stored array before the copy. No behaviour change: http_get_last_response_headers() already returned the outer request's headers. Test: ext/standard/tests/http/http_response_header_nested_request.phpt (fails on PHP-8.4 debug without the fix with the leak report, passes with it). The leak report comes from debug builds; a release build reports the leak only under ASAN or valgrind.