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#### Describe the bug
In v1, accessing the 'Set-Cookie' header in a response interceptor yields the raw string value of the header.

#### To Reproduce

```js
const axios = require('axios'),
      http = require('http');

const server = http
        .createServer((req, res) => {
          res.setHeader('Set-Cookie', 'my=value');
          res.writeHead(200);
          res.write('Hi there');
          res.end();
        })
        .listen(0),
      request = axios.create();

request.interceptors.response.use((res) => {
  console.log(res.headers['set-cookie']);
});

request({ url: `http://localhost:${server.address().port}` }).then(() => server.close());
```

The produces `my=value`

#### Expected behavior
`[ 'my=value' ]`

#### Environment
 - Axios Version [e.g. 0.18.0]: 1.0.0
 - Adapter [e.g. XHR/HTTP]: http
 - Browser [e.g. Chrome, Safari]: N/A
 - Browser Version [e.g. 22]: N/A
 - Node.js Version [e.g. 13.0.1]: 16.13.0
 - OS: [e.g. iOS 12.1.0, OSX 10.13.4]: Ubuntu 20.04
 - Additional Library Versions [e.g. React 16.7, React Native 0.58.0]: N/A

#### Additional context/Screenshots

N/A
index.d.ts

type AxiosHeaderValue = string | string[] | number | boolean | null;
type RawAxiosHeaders = Record<string, AxiosHeaderValue>;
type MethodsHeaders = {
  [Key in Method as Lowercase<Key>]: AxiosHeaders;
};
interface CommonHeaders  {
  common: AxiosHeaders;
}
type AxiosHeaderMatcher = (this: AxiosHeaders, value: string, name: string, headers: RawAxiosHeaders) => boolean;
type AxiosHeaderSetter = (value: AxiosHeaderValue, rewrite?: boolean | AxiosHeaderMatcher) => AxiosHeaders;
type AxiosHeaderGetter = ((parser?: RegExp) => RegExpExecArray | null) |
    ((matcher?: AxiosHeaderMatcher) => AxiosHeaderValue);
type AxiosHeaderTester = (matcher?: AxiosHeaderMatcher) => boolean;
export class AxiosHeaders {
  constructor(
      headers?: RawAxiosHeaders | AxiosHeaders,
      defaultHeaders?: RawAxiosHeaders | AxiosHeaders
  );
  set(headerName?: string, value?: AxiosHeaderValue, rewrite?: boolean | AxiosHeaderMatcher): AxiosHeaders;
  set(headers?: RawAxiosHeaders | AxiosHeaders, rewrite?: boolean): AxiosHeaders;
  get(headerName: string, parser: RegExp): RegExpExecArray | null;
  get(headerName: string, matcher?: true | AxiosHeaderMatcher): AxiosHeaderValue;
  has(header: string, matcher?: true | AxiosHeaderMatcher): boolean;
  delete(header: string | string[], matcher?: AxiosHeaderMatcher): boolean;
  clear(): boolean;
  normalize(format: boolean): AxiosHeaders;
  toJSON(): RawAxiosHeaders;
  static from(thing?: AxiosHeaders | RawAxiosHeaders | string): AxiosHeaders;
  static accessor(header: string | string[]): AxiosHeaders;
  setContentType: AxiosHeaderSetter;
  getContentType: AxiosHeaderGetter;
  hasContentType: AxiosHeaderTester;
  setContentLength: AxiosHeaderSetter;
  getContentLength: AxiosHeaderGetter;
  hasContentLength: AxiosHeaderTester;
  setAccept: AxiosHeaderSetter;
  getAccept: AxiosHeaderGetter;
  hasAccept: AxiosHeaderTester;
  setUserAgent: AxiosHeaderSetter;
  getUserAgent: AxiosHeaderGetter;
  hasUserAgent: AxiosHeaderTester;
  setContentEncoding: Axios