Force X4 root in chain before it becomes default

[Osiris]

From the reply in that latter post:

@jsha

We don't have the exact date set - we're waiting on a cross-sign from IdenTrust, but it will be sometime this fall.

From Chain of Trust:

• Active
  • Let’s Encrypt Authority X3 ( RSA 2048, O = Let's Encrypt, CN = Let's Encrypt Authority X3 )
    • Signed by ISRG Root X1: der, pem, txt
    • Cross-signed by IdenTrust: der, pem, txt
  • Let’s Encrypt R3 ( RSA 2048, O = Let's Encrypt, CN = R3 )
    • Signed by ISRG Root X1: der, pem, txt
    • Cross-signed by IdenTrust: der, pem, txt

My eyes spot a cross-signed R3 intermediate! It was added to the website 18 hours ago.