[BUG] typescript-fetch openapi generator fails out-of-the-box

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

I added this to my package.json:
"@openapitools/openapi-generator-cli": "^2.3.10",
and when I run this command:
"generate:api": "(rm -rf src/api/gen || rmdir src/api/gen /s /q) && openapi-generator-cli generate -g typescript-fetch --additional-properties=supportsES6=true,typescriptThreePlus=true -i ../openapi/schema.yaml -o ./src/api/gen"
I get the following error:

Failed to compile.

/##/runtime.ts
TypeScript error in /###/runtime.ts(152,3):
Type '((input: RequestInfo, init?: RequestInit | undefined) => Promise<Response>) | undefined' is not assignable to type '(input: RequestInfo, init?: RequestInit | undefined) => Promise<Response>'.
  Type 'undefined' is not assignable to type '(input: RequestInfo, init?: RequestInit | undefined) => Promise<Response>'.  TS2322

    150 | 
    151 |     get fetchApi(): FetchAPI {
  > 152 |               return this.configuration.fetchApi;
        |               ^
    153 |     }
    154 | 
    155 |     get middleware(): Middleware[] {

When I add "as FetchAPI" to line 152, everything works correctly. I have no idea where the problem is. Why does it generate code with this error?

openapi-generator version

2.3.10

OpenAPI declaration file content or url

N/A

Generation Details

N/A

Steps to reproduce

N/A

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/10164
https://github.com/OpenAPITools/openapi-generator/pull/10216 - supposedly it was fixed but it's still an issue when using version 2.3.10

Suggest a fix

Not sure about the fix. I quickly worked around it by casting it "as FetchAPI" which is not a good solution:

    150 | 
    151 |     get fetchApi(): FetchAPI {
   152 |               return this.configuration.fetchApi as FetchAPI;
        |               
    153 |     }

Start by reproducing the package.json command with @openapitools/openapi-generator-cli 2.3.10 and inspect the generated runtime.ts at line 152. Compare the failure with related issue 10164 and PR 10216; done means typescript-fetch output compiles without a manual FetchAPI cast.