Use new QBA::assign in QXcbMime::mimeDataForAtom

QByteArray::assign() re-uses existing unshared capacity(), if any, and
is therefore potentially more efficient than '= QByteArray(~)' (and
never slower).

Task-number: QTBUG-106201
Pick-to: 6.6
Change-Id: I5e5114064c8aaa23892e95c235335632d7c5cd0a
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/plugins/platforms/xcb/qxcbmime.cpp

@@ -79,8 +79,7 @@ bool QXcbMime::mimeDataForAtom(QXcbConnection *connection, xcb_atom_t a, QMimeDa
         if (atomName == "text/uri-list"_L1
             && connection->atomName(a) == "text/x-moz-url") {
             const QString mozUri = QLatin1StringView(data->split('\n').constFirst()) + u'\n';
-            *data = QByteArray(reinterpret_cast<const char *>(mozUri.data()),
-                               mozUri.size() * 2);
+            data->assign({reinterpret_cast<const char *>(mozUri.data()), mozUri.size() * 2});
         } else if (atomName == "application/x-color"_L1)
             *dataFormat = 16;
         ret = true;