[testmode] Fix types of `wrapRequestHandler` (#80055)
Was previously shadowed because we used an uncast `require` which results in `any`.
Fixes
```
Argument of type '<T>(request: NextRequestHint, fn: () => T) => T' is not assignable to parameter of type '(req: Request, fn: () => T) => T'.
Types of parameters 'request' and 'req' are incompatible.
Type 'Request' is missing the following properties from type 'NextRequestHint': sourcePage, fetchMetrics, request, respondWith, and 6 more.ts(2345)
```
