[BUG][typescript-fetch] middleware.onError does not handle errors from statuses like 401

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Pre-question: Regarding semantic errors, should we classify a response status such as 401 as an error? If yes, there seems to be a bug.

I observed that the middleware.onError does not handle errors from response status codes like 401. Upon reviewing the TypeScript code, I noticed how the response is validated

    protected async request(context: RequestOpts, initOverrides?: RequestInit | InitOverrideFunction): Promise<Response> {
        const { url, init } = await this.createFetchParams(context, initOverrides);
        const response = await this.fetchApi(url, init);
        if (response && (response.status >= 200 && response.status < 300)) {
            return response;
        }
        throw new ResponseError(response, 'Response returned an error code');
    }

but middleware.onError is inside fetchApi function, so it can't be handled properly.

Steps to reproduce

Setup any onError middleware and get response.status == 401 from network call

Suggest a fix

If we consider response.status == 401 as an error, we should verify statuses within the fetchApi function. This way, in the catch block, the response can be sent to middleware.onError.

If the suggestion will be approved, I can work on this issue.

Start with the TypeScript fetch implementation's fetchApi and request methods shown in the report, then reproduce a network response with status 401 using an onError middleware. Confirm whether non-2xx responses should be treated as errors, and consider the issue done when the middleware receives the resulting ResponseError and the relevant behavior is covered by a test.