lang/ruby30: Update pkg-message
In Ruby 3.0 following standard libraries are distributed as bundled
gems.
- minitest
- power_assert
- test-unit
- typeprof
- rexml
- rss
But this port doesn't include bundled gems in its package. So add
message to pkg-message that they are provided as separate ports.
PR: 259757
Approved by: maintainer timeout (> 3 weeks)