Some JVM indexes fail when passed without specifying the distro on aarch64

[Gedochao]

I'm not yet 100% sure where should we fix it.
Technically speaking, cs defaults to adoptium everywhere, so the error it fails with is valid...

cs java-home --jvm 16 --architecture arm64
# JVM 16 not found in index: No adoptium version matching '1.16+' found

I don't think we should fail in Scala CLi under the same circumstances, however.
Perhaps we should just log that the index wasn't found for adoptium, and fallback to smth else (i.e. zulu)...

Originally posted by @Gedochao in #3375 (comment)

So some JVM indexes (i.e. 16 for aarch64) aren't available for adoptium, which is the default for coursier.
We should do one of the following:

• log a warning and fallback to another distro (i.e. zulu)
• keep failing from Scala CLI, but provide alternatives in the error message