include service-worker.js in manifest

[Rich-Harris]

fixes #3187. service-worker.js is an anomaly because it's a generated file, but it lives among the contents of static, so it was overlooked previously. No test because the effects are only really observable in certain production environments (Cloudflare specifically, because the handler itself is responsible for serving assets), depending on how they work

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Latest commit: ec867f9

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[dreitzner]

lgtm