### 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` 

test/module/typings/esm/index.ts
(data: any) => ({ baz: 'qux' })
  ],
  headers: { 'X-FOO': 'bar' },
  params: { id: 12345 },
  paramsSerializer: {
    indexes: true,
    encode: (value: any) => value,
    serialize: (value: Record<string, any>, options?: ParamsSerializerOptions) => String(value)
  },
  data: { foo: 'bar' },
  timeout: 10000,
  withCredentials: true,
  auth: {
    username: 'janedoe',
    password: 's00pers3cret'
  },
  responseType: 'json',
  xsrfCookieName: 'XSRF-TOKEN',
  xsrfHeaderName: 'X-XSRF-TOKEN',
  onUploadProgress: (progressEvent: AxiosProgressEvent) => {},
  onDownloadProgress: (progressEvent: AxiosProgressEvent) => {},
  maxContentLength: 2000,
  maxBodyLength: 2000,
  validateStatus: (status: number) => status >= 200 && status < 300,
  maxRedirects: 5,
  proxy: {
    host: '127.0.0.1',
    port: 9000
  },
  cancelToken: new axios.CancelToken((cancel: Canceler) => {})