fix: X-Forwarded-Proto rejected when allowedDomains includes protocol and hostname
The protocol validation in validateForwardedHeaders() passed the full pattern
object to matchPattern(), which also checked hostname against the hardcoded
test URL (example.com). Pass only { protocol } to matchPattern() so that only
the protocol field is validated; the host+proto combination is already checked
in the host validation block below.
Fixes withastro/astro#15559