builtins: QUrl exetends URL, not Url

Url doesn't seem to exist, where as URL is part of one of the web API
extension which  we support in QML.

Pick-to: 6.6 6.5
Change-Id: Ieebcf603b8497315fd8039f6b01fbc0f11f1a3a9
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/imports/builtins/builtins.qmltypes

@@ -280,7 +280,7 @@ Module {
 
     Component {
         name: "QUrl"
-        extension: "Url"
+        extension: "URL"
         exports: ["QML/url 1.0"]
         exportMetaObjectRevisions: [256]
         accessSemantics: "value"