Fix check for header_up

[yubiuser]

PR #7454 changed the header from header_up Host {hostport} to header_up Host {upstream_hostport} when reverse_proxy for HTTPS.

However, the PR forgot to change a parser check to the new default. This results in logspam when users revert to the old behavior setting header_up Host {hostport}. Caddy starts to warn about unnecessary header_up being doubled - while this is not true anymore.

No AI was used.

[CLAassistant]

All committers have signed the CLA.

[francislavoie]

The change is not quite right, it needs to take into account that hostport is only passed for HTTPS and not HTTP.

[yubiuser]

Thanks, you're correct. I've added a commit that checks if the commonScheme is https and only in this case performs the check.