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#### Describe the bug

`config.paramsSerializer.indexes = false` (default) adds indexes if an object is inside an array but it shouldn't.

#### To Reproduce

https://runkit.com/doits/634530f2d3a446000813ef73

```js
var axios = require("axios")

const req = await axios.get('https://www.example.com', { params: { a: [{ name: 'abc' }], b: ['x', 'y'] } })

console.log(req.request.path)

// => "/?a[0][name]=abc&b[]=x&b[]=y"
```

#### Expected behavior

No `a[0]` but `a[]`:

```js
// => "/?a[][name]=abc&b[]=x&b[]=y"
```

#### Environment
 - Axios Version 1.1.2

#### Additional context/Screenshots

None

lib/helpers/buildURL.js
'use strict';
import utils from '../utils.js';
import AxiosURLSearchParams from '../helpers/AxiosURLSearchParams.js';
/**
 * It replaces all instances of the characters `:`, `$`, `,`, `+`, `[`, and `]` with their
 * URI encoded counterparts
 *
 * @param {string} val The value to be encoded.
 *
 * @returns {string} The encoded value.
 */
function encode(val) {
  return encodeURIComponent(val).
    replace(/%3A/gi, ':').
    replace(/%24/g, '$').
    replace(/%2C/gi, ',').
    replace(/%20/g, '+').
    replace(/%5B/gi, '[').
    replace(/%5D/gi, ']');
}
/**
 * Build a URL by appending params to the end
 *
 * @param {string} url The base of the url (e.g., http://www.google.com)
 * @param {object} [params] The params to be appended
 * @param {?object} options
 *
 * @returns {string} The formatted url
 */
export default function buildURL(url, params, options) {