chore: update/simplify test

[Rich-Harris]

realised we can simplify this a bit while looking into #16612 etc

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[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16630

[dummdidumm]

you should be able to do the same for the next test that is the same except for using $effect.pre instead of $effect

[Rich-Harris]

good catch, done