test(h3): rebuild h3client harness when source is newer than binary

A stale h3client binary (predating #48, which unstalled response bodies
> ~1 MiB) silently fails 028-h3-large-body and 032-h3-connection-migration
with len=0 — looking like a server regression when the server is fine.

SKIPIF only rebuilt the harness when the binary was missing, never when
h3client.c had moved ahead of it. Rebuild on mtime staleness too.

Author: EdmondDantes

tests/phpt/server/h3/_h3_skipif.inc

@@ -68,8 +68,14 @@ function h3_skipif(array $req = []): void {
             die('skip h3client harness is POSIX-only');
         }
         $client = __DIR__ . '/../../../h3client/h3client';
-        if (!is_executable($client)) {
-            $src = __DIR__ . '/../../../h3client/h3client.c';
+        $src = __DIR__ . '/../../../h3client/h3client.c';
+        /* Rebuild when the binary is missing OR the source is newer than
+         * it: a stale binary from before a harness fix silently fails the
+         * E2E tests (e.g. #48 unstalled bodies > 1 MiB — an old binary
+         * still returns len=0 on 028/032 and looks like a server bug). */
+        $stale = is_file($src) && is_file($client)
+              && @filemtime($src) > @filemtime($client);
+        if (!is_executable($client) || $stale) {
             if (!is_file($src)) {
                 die('skip h3client source missing');
             }