Try alternative PHP 8.1 strftime test fix

Author: onli

tests/include/functionsSmartyTest.php

@@ -117,7 +117,7 @@ public function test_smarty_renders_formatTime()
 
         serendipity_smarty_init();
 
-        setlocale(LC_ALL, 'en_US');
+        Locale::setDefault('en_US_POSIX');
         $template_string = '{946684800|@formatTime:\'%b %e. %Y\'}';
         $result = $serendipity['smarty']->fetch('eval:' . $template_string);
         $this->assertEquals('Jan  1. 2000', $result);