[UxSite] Back button with Swup on the demo page

[weaverryan]

From Ondřej Frei on the blog post comments: https://symfony.com/blog/hello-ux-symfony-com-and-4-new-ux-components#comments

A minor bug report: Go to https://ux.symfony.com/, click Swup Integration, click the back button in the browser and then click Swup Integration again. The "/swup" slug just shortly appears in the URL and is gone again, the Swup Integration page is not shown at all (only the first time, before the browser's Back button).

From me:

We are "mixing" Turbo and Swup on that page (which normally makes no sense because they are technologies that do the same thing), so that might be causing an issue. If so, we can change to Swup only for that one page :).