Prevent from failing using an extra protocol in resolver's URL

[rolang]

Hi, after we added a resolver with a custom protocol in the URL, like artifactregistry://example.com/maven we got java.net.MalformedURLException exceptions from this plugin. I tried to change it to use java.net.URI instead, but it was throwing exceptions in another place, so I tried to get the host from one of them as in this PR and it seemed to work.

Example URL/URI outputs:

scala> URI("artifactregistry://example.com").getHost
val res2: String = example.com
                                                                                                                                                                                                                 
scala> URL("artifactregistry://example.com").getHost
java.net.MalformedURLException: unknown protocol: artifactregistry

Related PR on extra protocol handlers: scala-steward-org/scala-steward#2628

[fthomas]

LGTM. Thanks @rolang!