Fix parallel test race condition in lib.inc temp dir creation

tempnam(__DIR__, '.tmp') + unlink + mkdir has a TOCTOU window: another
parallel worker can call tempnam and get the same name after unlink but
before mkdir. With -j8 and all tests sharing __DIR__ (the run-tests
--temp-source/target dir), this reliably causes "File exists" and
"Resource temporarily unavailable" failures on Windows.

Replace with a loop on mkdir using PID + uniqid: the PID isolates each
concurrent test process, and mkdir is atomic so no window exists.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: cataphract

tests/lib.inc

@@ -3,9 +3,10 @@
 function get_temp_dir() {
 	static $dir;
 	if (!$dir) {
-		$dir = tempnam(__DIR__, '.tmp');
-		unlink($dir);
-		mkdir($dir);
+		do {
+			$dir = sys_get_temp_dir() . DIRECTORY_SEPARATOR
+				. 'phpla_' . getmypid() . '_' . uniqid();
+		} while (!@mkdir($dir, 0700));
 
 		register_shutdown_function(function() use ($dir) {
 			$files = new RecursiveIteratorIterator(