[BUG] [typescript-fetch] header is not included in "get" methods

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

when the client is generated with typescript-fetch in the "get" methods, the headers included in the definition are not being added.

openapi-generator version

5.2.1

OpenAPI declaration file content or URL

https://petstore.swagger.io/v2/swagger.json

Generation Details

findPetsByStatus(status: Array<'available' | 'pending' | 'sold'>, options: any = {}): FetchArgs {
  // verify required parameter 'status' is not null or undefined
  if (status === null || status === undefined) {
      throw new RequiredError('status','Required parameter status was null or undefined when calling findPetsByStatus.');
  }
  const localVarPath = `/pet/findByStatus`;
  const localVarUrlObj = url.parse(localVarPath, true);
  const localVarRequestOptions = Object.assign({ method: 'GET' }, options);
  const localVarHeaderParameter = {} as any;
  const localVarQueryParameter = {} as any;

  // authentication petstore_auth required
  // oauth required
  if (configuration && configuration.accessToken) {
const localVarAccessTokenValue = typeof configuration.accessToken === 'function'
? configuration.accessToken("petstore_auth", ["write:pets", "read:pets"])
: configuration.accessToken;
      localVarHeaderParameter["Authorization"] = "Bearer " + localVarAccessTokenValue;
  }

  if (status) {
      localVarQueryParameter['status'] = status;
  }

  localVarUrlObj.query = Object.assign({}, localVarUrlObj.query, localVarQueryParameter, options.query);
  // fix override query string Detail: https://stackoverflow.com/a/7517673/1077943
  delete localVarUrlObj.search;
  localVarRequestOptions.headers = Object.assign({}, localVarHeaderParameter, options.headers);

  return {
      url: url.format(localVarUrlObj),
      options: localVarRequestOptions,
  };
}

This method should include:

['application/json', 'application/xml'];

Steps to reproduce

Related issues/PRs

Suggest a fix

Generate a typescript-fetch client from the linked Petstore OpenAPI declaration and inspect the generated findPetsByStatus GET method shown in the issue. Compare its request headers with the operation definition; done means the generated method includes the declared ['application/json', 'application/xml'] header values.