### 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
Error | unknown,
    code?: string,
    config?: AxiosRequestConfig<D>,
    request?: any,
    response?: AxiosResponse<T, D>,
    customProps?: object,
): AxiosError<T, D>;
  static readonly ERR_FR_TOO_MANY_REDIRECTS = "ERR_FR_TOO_MANY_REDIRECTS";
  static readonly ERR_BAD_OPTION_VALUE = "ERR_BAD_OPTION_VALUE";
  static readonly ERR_BAD_OPTION = "ERR_BAD_OPTION";
  static readonly ERR_NETWORK = "ERR_NETWORK";
  static readonly ERR_DEPRECATED = "ERR_DEPRECATED";
  static readonly ERR_BAD_RESPONSE = "ERR_BAD_RESPONSE";
  static readonly ERR_BAD_REQUEST = "ERR_BAD_REQUEST";
  static readonly ERR_NOT_SUPPORT = "ERR_NOT_SUPPORT";
  static readonly ERR_INVALID_URL = "ERR_INVALID_URL";
  static readonly ERR_CANCELED = "ERR_CANCELED";
  static readonly ECONNABORTED = "ECONNABORTED";
  static readonly ETIMEDOUT = "ETIMEDOUT";
}
export class CanceledError<T> extends AxiosError<T> {
}
export type AxiosPromise<T = any> = Promise<AxiosResponse<T>>;
export interface CancelStatic {
  new (message?: string): Cancel;
}
export interface Cancel {
  message: string | undefined;
}
export interface Canceler {
  (message?: string, config?: AxiosRequestConfig, request?: any): void;
}
export interface CancelTokenStatic {
  new (executor: (cancel: Canceler) => void): CancelToken;
  source(): CancelTokenSource;
}
export interface CancelToken {
  promise: Promise<Cancel>;
  reason?: Cancel;
  throwIfRequested(): void;
}
export interface CancelTokenSource {
  token: CancelToken;
  cancel: Canceler;
}
export interface AxiosInterceptorOptions {
  synchronous?: boolean;
  runWhen?: (config: AxiosRequestConfig) => boolean;
}
export interface AxiosInterceptorManager<V> {
  use(onFulfilled?: ((value: V) => V | Promise<V>) | null, onRejected?: ((error: any) => any) | null, options?: AxiosInterceptorOptions): number;
  eject(id: number): void;
  clear(): void;
}
export class Axios {
  constructor(config?: AxiosRequestConfig);
  defaults: AxiosDefaults;
  interceptors: {
    request: AxiosInterceptorMa