fix(HttpResponse): skip setting "Content-Length" if it is already set

[kettanaito]

When upgrading @mswjs/interceptors to 0.33 (in https://github.com/mswjs/msw/pull/2011), I've noticed a failing mocked binary response test: it was listing the Content-Length header value twice

Content-Length: 1044, 1044

[!WARNING] This indicates a deeper issue, as .set() on Headers instance must not join values. Something goes off here. Raw Headers from Undici behaved correctly on that branch.

We don't have any check if the Content-Length response header has already been set on HttpResponse.arrayBuffer(), which means MSW will disregard your custom Content-Length, which is a bug.

[kettanaito]

Released: v2.3.5 🎉

This has been released in v2.3.5!

• 📄 Release notes
• 📦 npm package

Make sure to always update to the latest version (npm i msw@latest) to get the newest features and bug fixes.

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