Reset url before updating page store

[Rich-Harris]

Alternative to #4773. We can keep the existing caching logic, we just need to make sure url isn't stale

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[Rich-Harris]

Ah whoops, I deleted the 'successfully preloads same route with different hashes many times' test in response to your since-deleted comment @tcc-sejohnson — was that a mistake?

[elliott-with-the-longest-name-on-github]

@Rich-Harris

Nope, all good -- I referenced the wrong lines in the comment and couldn't figure out how to update the reference, so I was just going to re-comment with the correct line references... you were just a bit too fast on the uptake. :)

[elliott-with-the-longest-name-on-github]

@Rich-Harris Quick note: Remember to close #4768 after this is merged -- the issue is no longer linked to the PR.