Icons metadata on Google Fonts API is not a valid JSON

**Describe the issue**
The Icons metadata returned by https://fonts.google.com/metadata/icons is not a valid JSON as it contains some random characters in the first line. Is this an expected behaviour?

**To Reproduce**
Download https://fonts.google.com/metadata/icons.

**Expected behavior**
Return a valid JSON

**Additional context**
*None*

**Screenshots**
The first lines of the returned data:
```json
)]}'
{
"host": "fonts.gstatic.com",
"asset_url_pattern": "/s/i/{family}/{icon}/v{version}/{asset}",
"families": [
"Material Icons",
"Material Icons Outlined",
"Material Icons Round",
"Material Icons Sharp",
"Material Icons Two Tone"
],
"icons": [
```