fix: does not work in Nuxt 3 dev-mode / with ipv6

When `is-https` is used in Nuxt 3 development mode with `--https --ssl-cert foo --ssl-key bar`
- `req.connection.encrypted` is not set, eventhough it should be
- `req.headers['x-forwarded-proto']` is equal to `IPv6`, eventhough it should be `https`

Trying the reproduction https://stackblitz.com/edit/github-jwgna1?file=app.vue the console only prints `undefined` for all console logs.

