Bug 1888488: update staging content signing root certificate to new cas_new root certificate  a=RyanVM

This is the cas_new root (https://bugzilla.mozilla.org/attachment.cgi?id=9390855) converted from PEM to DER with: `openssl x509 -in cas-new-root-2024-03-12.crt -inform PEM -outform DER`

Original Revision: https://phabricator.services.mozilla.com/D206040

Differential Revision: https://phabricator.services.mozilla.com/D207263