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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
lib/core/AxiosHeaders.js
});
Object.assign(AxiosHeaders, {
  from: function(thing) {
    if (utils.isString(thing)) {
      return new this(parseHeaders(thing));
    }
    return thing instanceof this ? thing : new this(thing);
  },
  accessor: function(header) {
    const internals = this[$internals] = (this[$internals] = {
      accessors: {}
    });
    const accessors = internals.accessors;
    const prototype = this.prototype;
    function defineAccessor(_header) {
      const lHeader = normalizeHeader(_header);
      if (!accessors[lHeader]) {
        buildAccessors(prototype, _header);
        accessors[lHeader] = true;
      }
    }
    utils.isArray(header) ? header.forEach(defineAccessor) : defineAccessor(header);
    return this;
  }
});
AxiosHeaders.accessor(['Content-Type', 'Content-Length', 'Accept', 'Accept-Encoding', 'User-Agent']);
utils.freezeMethods(AxiosHeaders.prototype);
utils.freezeMethods(AxiosHeaders);
export default AxiosHeaders;