Fix para tag in build/gen_stub.php

[ci skip]

<variablelist> is not valid within <simpara>, this should use <para>.
Regressed in 32789c0.

Author: ndossche

build/gen_stub.php

@@ -1813,7 +1813,7 @@ private function getParameterSection(DOMDocument $doc): DOMElement {
             $parametersRefSec->appendChild($noParamEntity);
             return $parametersRefSec;
         } else {
-            $parametersPara = $doc->createElement('simpara');
+            $parametersPara = $doc->createElement('para');
             $parametersRefSec->appendChild($parametersPara);
 
             $parametersPara->appendChild(new DOMText("\n   "));