drive.files.create creates a file with 0 bytes

#### Environment details

- OS: macOS 11.4
- Node.js version: 14.16.1
- npm version: 6.14.12
- `googleapis` version: 78.0.0

#### Description

Files uploaded to Google Drive using a stream or buffer have length of zero bytes. No errors anywhere. Works only when body is a string, but how do you make a string from a binary file and how do you specify the charset for a text file?

#### Steps to reproduce

```javascript
const { google } = require('googleapis');
const Readable = require('stream').Readable;

async function uploadToGoogle(googlePrivateKey) {
const scopes = [
'https://www.googleapis.com/auth/drive'
];

const auth = new google.auth.JWT(
***********@**********.iam.gserviceaccount.com', null,
googlePrivateKey, scopes
);

const drive = google.drive({ version: 'v3', auth });

const buffer = Buffer.from('Test data 1', 'latin1');

const driveFile = await drive.files.create({
requestBody: {
name: 'testfile.txt',
mimeType: 'text/plain',
parents: [
'***************************************'
],
supportsAllDrives: true
},
media: {
mimeType: 'text/plain',
body: new Readable(buffer)
}
});
}
```