Update `msv-core` dependency to `2022.7`

[cowtowncoder]

So: there has been a new cleaned up release of MSV, see:

https://mvnrepository.com/artifact/net.java.dev.msv/msv-core/2022.7

and we should upgrade the dependency. This likely requires at least a minor version bump to 6.4.0, although I guess there is the possibility of combining this with #134 -- that is probably safer?