<!-- Click "Preview" for a more readable version --

Please read and follow the instructions before submitting an issue:

- Read all our documentation, especially the [README](https://github.com/axios/axios/blob/master/README.md). It may contain information that helps you solve your issue.
- Ensure your issue isn't already [reported](https://github.com/axios/axios/issues?utf8=%E2%9C%93&q=is%3Aissue).
- If you aren't sure that the issue is caused by Axios or you just need help, please use [Stack Overflow](https://stackoverflow.com/questions/tagged/axios) or [our chat](https://gitter.im/mzabriskie/axios).
- If you're reporting a bug, ensure it isn't already fixed in the latest Axios version.
- Don't remove any title of the issue template, or it will be treated as invalid by the bot.

⚠️👆 Feel free to these instructions before submitting the issue 👆⚠️
-->

#### 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/toFormData.js
const stack = [];
  const exposedHelpers = Object.assign(predicates, {
    defaultVisitor,
    convertValue,
    isVisitable
  });
  function build(value, path) {
    if (utils.isUndefined(value)) return;
    if (stack.indexOf(value) !== -1) {
      throw Error('Circular reference detected in ' + path.join('.'));
    }
    stack.push(value);
    utils.forEach(value, function each(el, key) {
      const result = !utils.isUndefined(el) && visitor.call(
        formData, el, utils.isString(key) ? key.trim() : key, path, exposedHelpers
      );
      if (result === true) {
        build(el, path ? path.concat(key) : [key]);
      }
    });
    stack.pop();
  }
  if (!utils.isObject(obj)) {
    throw new TypeError('data must be an object');
  }
  build(obj);
  return formData;
}
export default toFormData;