chore(deps): update dependency svelte to ^5.21.0 [skip ci]

This MR contains the following updates:

Package	Type	Update	Change
svelte (source)	devDependencies	minor	^5.20.5 -> ^5.21.0

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Release Notes

sveltejs/svelte (svelte)

v5.21.0

Compare Source

Minor Changes

• chore: Reduce hydration comment for {:else if} (#​15250)

Patch Changes

• fix: disallow bind:group to snippet parameters (#​15401)

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