fix: use Bun's Fetch interface for fetch

[ragavpr]

Allows TypeScript to use Bun's FetchRequestInit instead of Node's RequestInit in fetch request options.

What does this PR do?

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

I modified the .d.ts file directly in my own project's node_modules and verified the type is recognized correctly in VSCode.

Additional Info

This previously existing similar type probably supports, fetch to be of Fetch, hence made this change

bun/packages/bun-types/globals.d.ts

Line 945 in 3d68a94

var fetch: Fetch;

Fixes #13827