Fix GH-11630: proc_nice_basic.phpt only works at certain nice levels

Closes GH-11635.

Author: nielsdos

ext/standard/tests/general_functions/proc_nice_basic.phpt

@@ -30,7 +30,9 @@ if ($exit_code !== 0) {
     $niceBefore = getNice($pid);
     proc_nice($delta);
     $niceAfter = getNice($pid);
-    var_dump($niceBefore == ($niceAfter - $delta));
+    // The maximum niceness level is 19, if the process is already running at a high niceness, it cannot be increased.
+    // Decreasing is only possible for superusers.
+    var_dump(min($niceBefore + $delta, 19) == $niceAfter);
 ?>
 --EXPECT--
 bool(true)