Fix unseekable test (#391)

Author: maennchen

test/ZipStreamTest.php

@@ -327,11 +327,14 @@ public function testAddFileFromStreamUnseekableInputWithoutZeroHeader(): void
             defaultEnableZeroHeader: false,
         );
 
-        if (file_exists('/dev/null')) {
-            $streamUnseekable = fopen('/dev/null', 'w+');
-        } elseif (file_exists('NUL')) {
-            $streamUnseekable = fopen('NUL', 'w+');
-        } else {
+        foreach (['cat', 'more'] as $cmd) {
+            $streamUnseekable = @popen($cmd, 'w');
+            if ($streamUnseekable !== false) {
+                break;
+            }
+        }
+
+        if ($streamUnseekable === false) {
             $this->markTestSkipped('Needs file /dev/null');
         }