🐛 BUG: Responses from fetchMock do not have immutable headers

[tyler-goodwin]

Which Cloudflare product(s) does this pertain to?

Workers Vitest Integration

What version(s) of the tool(s) are you using?

0.5.2 [Vitest Pool Workers], 2.0.5 [vitest], 3.60.3 [wrangler]

What version of Node are you using?

20.12.0

What operating system and version are you using?

Mac OS 15.1.1

Describe the Bug

Observed behavior

Responses from fetchMock do not have immutable headers like when running in the workers runtime for a deployed worker

Expected behavior

Responses from fetchMock should have immutable headers

Steps to reproduce

Run npm test in repro repo

Please provide a link to a minimal reproduction

https://github.com/tyler-goodwin/immutable-headers-repro/tree/main

Please provide any relevant error logs

No response