docs: mention update method on svelte-action page

[jamesscottbrown]

This mentions that a Svelte action can return an object with an update method.

Without this it's easy for someone who hasn't read the corresponding Reference page to mis-interpret the previous sentence as meaning that there is no mechanism for automatically re-running or updating actions when arguments change.

Preview of the edited page: https://svelte-dev-git-preview-svelte-15977-svelte.vercel.app/docs/svelte/use

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15977-svelte.vercel.app/

[MotionlessTrain]

Doesn’t the sentence just below this also mention the update method?
When using an $effect, the update method is not needed, as the effect would rerun when one of its dependencies change, which is probably why the update method is only mentioned in the legacy part

[jamesscottbrown]

Doesn’t the sentence just below this also mention the update method?

That's true - I initially missed this sentence as it was in a "legacy mode" box, and I had collapsed these.