4.3 Regression / Model Admin search no longer updates URL

[stephenmcm]

When searching within a model admin in the CMS the page URL no longer updates this makes sharing links to deep searches impossible.

To recreate open a model admin on a SilverStripe 4.3 site and search in 4.2 and below the URL will update to contain a search query something like: `?q%5BSearchIndex%5D=Test``, this is no longer the case in 4.3.