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

tempnam(__DIR__, '.tmp') + unlink + mkdir has a TOCTOU window: after
unlink, another parallel worker's tempnam can claim the same name. With
all tests sharing __DIR__ (the run-tests --temp-source/target dir),
this reliably causes "File exists" collisions on Windows.

Use sys_get_temp_dir() + PID + uniqid() instead: these together make
collision impossible, so no retry loop is needed.

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

Author: cataphract

tests/lib.inc

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