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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
HeaderSetter;
  getContentEncoding: AxiosHeaderGetter;
  hasContentEncoding: AxiosHeaderTester;
}
export type RawAxiosRequestHeaders = Partial<RawAxiosHeaders & MethodsHeaders & CommonHeaders>;
export type AxiosRequestHeaders = Partial<RawAxiosHeaders & MethodsHeaders & CommonHeaders> & AxiosHeaders;
export type RawAxiosResponseHeaders = Partial<Record<string, string> & {
  "set-cookie"?: string[]
}>;
export type AxiosResponseHeaders = RawAxiosResponseHeaders & AxiosHeaders;
export interface AxiosRequestTransformer {
  (this: AxiosRequestConfig, data: any, headers: AxiosRequestHeaders): any;
}
export interface AxiosResponseTransformer {
  (this: AxiosRequestConfig, data: any, headers: AxiosResponseHeaders, status?: number): any;
}
export interface AxiosAdapter {
  (config: AxiosRequestConfig): AxiosPromise;
}
export interface AxiosBasicCredentials {
  username: string;
  password: string;
}
export interface AxiosProxyConfig {
  host: string;
  port: number;
  auth?: {
    username: string;
    password: string;
  };
  protocol?: string;
}
export enum HttpStatusCode {
  Continue = 100,
  SwitchingProtocols = 101,
  Processing = 102,
  EarlyHints = 103,
  Ok = 200,
  Created = 201,
  Accepted = 202,
  NonAuthoritativeInformation = 203,
  NoContent = 204,
  ResetContent = 205,
  PartialContent = 206,
  MultiStatus = 207,
  AlreadyReported = 208,
  ImUsed = 226,
  MultipleChoices = 300,
  MovedPermanently = 301,
  Found = 302,
  SeeOther = 303,
  NotModified = 304,
  UseProxy = 305,
  Unused = 306,
  TemporaryRedirect = 307,
  PermanentRedirect = 308,
  BadRequest = 400,
  Unauthorized = 401,
  PaymentRequired = 402,
  Forbidden = 403,
  NotFound = 404,
  MethodNotAllowed = 405,
  NotAcceptable = 406,
  ProxyAuthenticationRequired = 407,
  RequestTimeout = 408,
  Conflict = 409,
  Gone = 410,
  LengthRequired = 411,
  PreconditionFailed = 412,
  PayloadTooLarge = 413,
  UriTooLong = 414,
  UnsupportedMediaType = 415,
  RangeNotSatisfiable = 416,
  ExpectationFailed = 41