Even when explicitly passing https, registry requests to localhost are downgraded to http

### Description

`nerdctl login https://127.0.0.1:5000` will always be downgraded to http://127.0.0.1:5000

It seems to be because of the faulty logic in `remotes/docker/config/hosts.go` that apparently considers "the scheme is ambiguous" as the port is non-standard and the host is localhost.

Whether they fixed it for 2.0 is unclear to me at this point.

### Steps to reproduce the issue

1. `nerdctl login https://127.0.0.1:5000`

### Describe the results you received and expected

Seeing: request downgraded to http://127.0.0.1:5000

Should see: not downgraded, the scheme is explicit

### What version of nerdctl are you using?

1.7.6 / main

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_