### 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
})();
const fn1 = (a: number, b: number, c: number) => `${a}-${b}-${c}`;
const fn2: (arr: number[]) => string = axios.spread(fn1);
(() => {
  const fn1 = (a: number, b: number, c: number) => `${a}-${b}-${c}`;
  const fn2: (arr: number[]) => string = spread(fn1);
})();
axios.get('/user')
  .then((response: AxiosResponse) => 'foo')
  .then((value: string) => {});
axios.get('/user')
  .then((response: AxiosResponse) => Promise.resolve('foo'))
  .then((value: string) => {});
axios.get('/user')
  .then((response: AxiosResponse) => 'foo', (error: any) => 'bar')
  .then((value: string) => {});
axios.get('/user')
  .then((response: AxiosResponse) => 'foo', (error: any) => 123)
  .then((value: string | number) => {});
axios.get('/user')
  .catch((error: any) => 'foo')
  .then((value: any) => {});
axios.get('/user')
  .catch((error: any) => Promise.resolve('foo'))
  .then((value: any) => {});
const source: CancelTokenSource = axios.CancelToken.source();
axios.get('/user', {
  cancelToken: source.token
}).catch((thrown: AxiosError | Cancel) => {
  if (axios.isCancel(thrown)) {