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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
;
  insecureHTTPParser?: boolean;
  env?: {
    FormData?: new (...args: any[]) => object;
  };
  formSerializer?: FormSerializerOptions;
}
export interface HeadersDefaults {
  common: RawAxiosRequestHeaders;
  delete: RawAxiosRequestHeaders;
  get: RawAxiosRequestHeaders;
  head: RawAxiosRequestHeaders;
  post: RawAxiosRequestHeaders;
  put: RawAxiosRequestHeaders;
  patch: RawAxiosRequestHeaders;
  options?: RawAxiosRequestHeaders;
  purge?: RawAxiosRequestHeaders;
  link?: RawAxiosRequestHeaders;
  unlink?: RawAxiosRequestHeaders;
}
export interface AxiosDefaults<D = any> extends Omit<AxiosRequestConfig<D>, 'headers'> {
  headers: HeadersDefaults;
}
export interface CreateAxiosDefaults<D = any> extends Omit<AxiosRequestConfig<D>, 'headers'> {
  headers?: RawAxiosRequestHeaders | Partial<HeadersDefaults>;
}
export interface AxiosResponse<T = any, D = any>  {
  data: T;
  status: number;
  statusText: string;
  headers: RawAxiosResponseHeaders | AxiosResponseHeaders;
  config: AxiosRequestConfig<D>;
  request?: any;
}
export class AxiosError<T = unknown, D = any> extends Error {
  constructor(
      message?: string,
      code?: string,
      config?: AxiosRequestConfig<D>,
      request?: any,
      response?: AxiosResponse<T, D>
  );
  config?: AxiosRequestConfig<D>;
  code?: string;
  request?: any;
  response?: AxiosResponse<T, D>;
  isAxiosError: boolean;
  status?: number;
  toJSON: () => object;
  cause?: Error;
  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_CA