Change fetch.json() type to unknown

[karlismelderis-mckinsey]

Summary

Follow NodeJS type and change to unknown

Expected vs. Actual Behavior

Please align with NodeJS fetch types

unknown is preferred over any and would be more precise because without validating received data one does not really know what has been received

Playground Link

No response

Browser Support

• This API is supported in at least two major browser engines (not two Chromium-based browsers).

Have Tried The Latest Releases

• This issue applies to the latest release of TypeScript.
• This issue applies to the latest release of @types/web.

Additional Context

No response

[HolgerJeromin]

This will break very much existing code.
See microsoft/TypeScript#60899 for more background

[saschanaz]

Yeah, this would be technically correct but would still be scary in terms of compatibility.