Prepare for usage of the new QDomDocument::setContent() overload

The new overloads will return QDomDocument::ParseResult, that is
explicitly convertible to bool, so get rid of the implicit conversion.

Task-number: QTBUG-104507
Change-Id: I3d47bc84186d7809bbf643ff6fd708f065ac28c9
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

tests/auto/core5/sax/qxmlinputsource/tst_qxmlinputsource.cpp

@@ -160,7 +160,7 @@ private slots:
         if (bodyBytesRead == bodyLength)
         {
             QDomDocument domDoc;
-            success = domDoc.setContent(body);
+            success = bool(domDoc.setContent(body));
             eventLoop.exit();
         }
     }