### Describe the bug

`AxiosHeaders` types makes it so trying to call methods on the instance raises a `typescript` compilation error.

<img width="1142" alt="image" src="https://user-images.githubusercontent.com/476069/209943677-fa7775e7-0f23-4b86-88ae-ad28df8c0533.png">

`AxiosRequestConfig.headers` can be either `RawAxiosRequestHeaders` or `AxiosHeaders`. `RawAxiosRequestHeaders`, being an alias of `Record<string, AxiosHeaderValue>` causes methods to not be callable.

### To Reproduce

Invoke any method on `AxiosRequestConfig.headers`.

### Code snippet

```js
const api = axios.create({ ... })

api.interceptors.request.use(req => {
  // Trying to access any method on `req.headers` will result in
  // a "This expression is not callable" TS error
  req.headers.set('foo', 'bar')
})
```


### Expected behavior

Should be able to call any method declared in `AxiosHeaders`.

### Environment

* `axios`: `1.2.2`
* `node`: `18.12.1`
* `typescript`: `4.9.4`
* macOS Ventura `13.1` 

index.d.ts

      key: string | number,
      path: null | Array<string | number>,
      helpers: FormDataVisitorHelpers
  ): boolean;
}
export interface SerializerOptions {
  visitor?: SerializerVisitor;
  dots?: boolean;
  metaTokens?: boolean;
  indexes?: boolean | null;
}
export interface FormSerializerOptions extends SerializerOptions {
}
export interface ParamEncoder {
  (value: any, defaultEncoder: (value: any) => any): any;
}
export interface CustomParamsSerializer {
  (params: Record<string, any>, options?: ParamsSerializerOptions): string;
}
export interface ParamsSerializerOptions extends SerializerOptions {
  encode?: ParamEncoder;
  serialize?: CustomParamsSerializer;
}
type MaxUploadRate = number;
type MaxDownloadRate = number;
type BrowserProgressEvent = any;
export interface AxiosProgressEvent {
  loaded: number;
  total?: number;
  progress?: number;
  bytes: number;
  rate?: number;
  estimated?: number;
  upload?: boolean;
  download?: boolean;
  event?: BrowserProgressEvent;
}
type Milliseconds = number;
type AxiosAdapterName = 'xhr' | 'http' | string;
type AxiosAdapterConfig = AxiosAdapter | AxiosAdapterName;
export interface AxiosRequestConfig<D = any> {
  url?: string;
  method?: Method | string;
  baseURL?: string;
  transformRequest?: AxiosRequestTransformer | AxiosRequestTransformer[];
  transformResponse?: AxiosResponseTransformer | AxiosResponseTransformer[];
  headers?: RawAxiosRequestHeaders | AxiosHeaders;
  params?: any;
  paramsSerializer?: ParamsSerializerOptions;
  data?: D;
  timeout?: Milliseconds;
  timeoutErrorMessage?: string;
  withCredentials?: boolean;
  adapter?: AxiosAdapterConfig | AxiosAdapterConfig[];
  auth?: AxiosBasicCredentials;
  responseType?: ResponseType;
  responseEncoding?: responseEncoding | string;
  xsrfCookieName?: string;
  xsrfHeaderName?: string;
  onUploadProgress?: (progressEvent: AxiosProgressEvent) => void;
  onDownloadProgress?: (progressEvent: AxiosProgressEvent) => void;
  maxContentLength?: number;
  vali