devel/mill Update to 0.9.6

Changelog:

• repl and console targets now support forkArgs and forkEnv
• Support for Scala 3 release candidates and new Scaladoc 3 tool
• Support for Scala.js on Scala 3
• Scala Native improvements
• Test runner now uses an args file to support running tests on Windows
• GenIdea: better supports source jars, full config contributions and provided/runtime dependencies
• Various dependency updates
• Documentation site reworked to support multiple release versions
• Improved CI setup to better test mill on Windows

PR: 254886
Reported by: freebsd-ports@jan0sch.de (maintainer)