Update dependency @sveltejs/kit to v2.5.21

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@sveltejs/kit (source)	2.5.20 -> 2.5.21

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Release Notes

sveltejs/kit (@​sveltejs/kit)

### [`v2.5.21`](https://togithub.com/sveltejs/kit/blob/HEAD/packages/kit/CHANGELOG.md#2521) [Compare Source](https://togithub.com/sveltejs/kit/compare/@sveltejs/kit@2.5.20...@sveltejs/kit@2.5.21) ##### Patch Changes - chore: package provenance ([#​12567](https://togithub.com/sveltejs/kit/pull/12567))

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