[web/request] Restore attribute setting for search_state This was dropped in 1f84295bfe95 when `search_state` attribute was turned into a property, but without a setter. So adding a setter here restoring previous behaviour, as some tests and cubes use it. Related to #4875761.

raise NotImplementedError("Cannot migrate such an old version. Use intermediate Cubiweb version (try 3.16.x)")