fix: hydrate multiple <svelte:head> elements correctly

[dummdidumm]

The head hydration anchor didn't update after hydrating the contents of one <svelte:head> element, which meant subsequent <svelte:head> elements would always start at the beginning of the head. This PR fixes that. The test was updated such that the shape of each <svelte:head> content is sufficiently different to throw an error if this wasn't fixed.

fixes #12458
fixes #12399

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Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

🦋 Changeset detected

Latest commit: a92e715

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

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