StudioWelcome: Fix QTC_ASSERT

Deleting QtcProcess instance directly from
one of its signal handlers will lead to crash.

Change-Id: Ida231f29dc6a717dfe4971da9743b1fb9b225495
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/studiowelcome/examplecheckout.cpp

@@ -503,7 +503,7 @@ bool DataModelDownloader::start()
                 QTC_ASSERT(archive->isValid(), delete archive; return );
                 QObject::connect(archive, &Utils::Archive::finished, this, [this, archive](bool ret) {
                     QTC_CHECK(ret);
-                    delete archive;
+                    archive->deleteLater();
                     emit finished();
                 });
                 archive->unarchive();