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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
7,
  ImATeapot = 418,
  MisdirectedRequest = 421,
  UnprocessableEntity = 422,
  Locked = 423,
  FailedDependency = 424,
  TooEarly = 425,
  UpgradeRequired = 426,
  PreconditionRequired = 428,
  TooManyRequests = 429,
  RequestHeaderFieldsTooLarge = 431,
  UnavailableForLegalReasons = 451,
  InternalServerError = 500,
  NotImplemented = 501,
  BadGateway = 502,
  ServiceUnavailable = 503,
  GatewayTimeout = 504,
  HttpVersionNotSupported = 505,
  VariantAlsoNegotiates = 506,
  InsufficientStorage = 507,
  LoopDetected = 508,
  NotExtended = 510,
  NetworkAuthenticationRequired = 511,
}
export type Method =
    | 'get' | 'GET'
    | 'delete' | 'DELETE'
    | 'head' | 'HEAD'
    | 'options' | 'OPTIONS'
    | 'post' | 'POST'
    | 'put' | 'PUT'
    | 'patch' | 'PATCH'
    | 'purge' | 'PURGE'
    | 'link' | 'LINK'
    | 'unlink' | 'UNLINK';
export type ResponseType =
    | 'arraybuffer'
    | 'blob'
    | 'document'
    | 'json'
    | 'text'
    | 'stream';
export type responseEncoding =
    | 'ascii' | 'ASCII'
    | 'ansi' | 'ANSI'
    | 'binary' | 'BINARY'
    | 'base64' | 'BASE64'
    | 'base64url' | 'BASE64URL'
    | 'hex' | 'HEX'
    | 'latin1' | 'LATIN1'
    | 'ucs-2' | 'UCS-2'
    | 'ucs2' | 'UCS2'
    | 'utf-8' | 'UTF-8'
    | 'utf8' | 'UTF8'
    | 'utf16le' | 'UTF16LE';
export interface TransitionalOptions {
  silentJSONParsing?: boolean;
  forcedJSONParsing?: boolean;
  clarifyTimeoutError?: boolean;
}
export interface GenericAbortSignal {
  readonly aborted: boolean;
  onabort?: ((...args: any) => any) | null;
  addEventListener?: (...args: any) => any;
  removeEventListener?: (...args: any) => any;
}
export interface FormDataVisitorHelpers {
  defaultVisitor: SerializerVisitor;
  convertValue: (value: any) => any;
  isVisitable: (value: any) => boolean;
}
export interface SerializerVisitor {
  (
      this: GenericFormData,
      value: any,
      key: string | number,
      path: null | Array<string | number>,
      helpers: FormDataVisitorHelpers
  ): boo