An install still on its legacy 3.11 venv runs its first `hermes update`
from that interpreter, which downloads uv and Python 3.14 with plain
urllib before PM's worker (and truststore) exists. Windows can cache Let's
Encrypt "Root YR" in its intermediate store without ISRG Root X1; GitHub's
asset CDN now chains through Root YR, so 3.11 rejected every download with
"unable to get issuer certificate" while PowerShell and 3.14 accepted it.
Python 3.13+ sets VERIFY_X509_PARTIAL_CHAIN by default. Set it on the PM
downloader's opener so the legacy interpreter applies the same rule;
hostname, expiry and pinned sha256 checks are unchanged.
Co-authored-by: Gille <4317663+helix4u@users.noreply.github.com>