lock version of werkzeug==2.0.3

Our unit tests were failing since yesterday as werkzeug has released a new version, and somewhere in our dependency chain we have werkzeug>=2.0 and we have installed 2.1.0. But it seems the tests designed by searx is only compatible with werkzeug==2.0.3. So hard locking the version fixes it. But this should not be an ideal fix, hence raised an issue at searx