Fix GH-8842 don't set sensitive param in legacy arginfo

Author: remicollet

build/gen_stub.php

@@ -1426,6 +1426,7 @@ public function discardInfoForOldPhpVersions(): void {
         foreach ($this->args as $arg) {
             $arg->type = null;
             $arg->defaultValue = null;
+            $arg->isSensitive = null;
         }
     }