OPTIMADE MaterialsCloud link may be outdated

I get

```
Error(s) during querying. Message(s) from server:
- 'CLIENT: Connection error or timeout.
URL: https://www.materialscloud.org/optimade/main/v1/links?filter=%28+link_type%3D%22child%22+OR+type%3D%22child%22+%29&response_format=json&page_limit=100&page_offset=0&page_number=1
Exception: SSLError(MaxRetryError("HTTPSConnectionPool(host=\'optimade.materialscloud.io\', port=443): Max retries exceeded with url: /main/index/v1/links?filter=%28+link_type%3D%22child%22+OR+type%3D%22child%22+%29&response_format=json&page_limit=100&page_offset=0&page_number=1 (Caused by SSLError(SSLCertVerificationError(1, \'[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self-signed certificate (_ssl.c:1129)\')))"))'
Please check the log and the server's validation status at https://www.optimade.org/providers-dashboard/.
```

Pinging @eimrek. Did something change?