fix: date test fail for some timezone

[adiguba]

The test for SvelteDate fail on some timezone, like mine (CEDT/CEST "France/Paris").

=> This is because the initial date is set to midnight, and the Date/UTCDate may differ based on the user timezone.

I changed the test in order to redo the same calculations with Date.
I think this should work on all timezone.

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[trueadm]

This looks better, thanks

[dummdidumm]

Omg thank you, this has been bugging my locally for weeks