Add forge now / Save code now: tabs are not preserved with the browser history

1. Go to https://archive.softwareheritage.org/save/
2. Click "Browse save requests"
3. Hit the back button

This does not bring me back to the "Help" tab, but stays on "Browse save request". Then refreshing the page brings me back to the "Help" tab (to match the lack of anchor in the URL)

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Migrated from T4051 (view on Phabricator)