Let's Encrypt root CA isn't working properly

### Prerequisites

- [x] I am running the latest version
- [x] I checked the documentation and found no answer
- [x] I checked to make sure that this issue has not already been filed
- Although https://github.com/AdguardTeam/AdGuardForSafari/issues/115 is related, this is narrower in scope and can be resolved separately

### Issue Details

* AdGuard for Safari version: 1.10.4 (macOS App Store) and 1.11.0 (beta)
* Environment name and version: Version 15.3 (16612.4.9.1.7, 16612)
* Operating System: macOS Big Sur 11.6.3 (20G415)
* Filters you use in AdGuard: A hand-made filter hosted on a website that uses a Let's Encrypt certificate
* Any other browser extensions you have installed: None

### Expected Behavior

After inputting the URL to a server using a Let's Encrypt certificate in a New filter subscription modal, clicking the Next button should not show an error.

### Actual Behavior

A modal shows displaying an error message:

```
Error occurred
Unfortunately, your custom filter cannot be added due to an unexpected error.
```

The terminal shows an error message with more details:

```
Error download filter by url , cause: Error: certificate has expired
```

### Screenshots

Screenshot:


### Additional Information

* One thing to try might be updating the Electron version in use: https://github.com/electron/electron/issues/31212

* Running AdGuard for Safari with the environment variable `NODE_TLS_REJECT_UNAUTHORIZED=0` resolves the issue but comes a self-evident drawback.