for now i fixed this issue. masked the ruby 2.2 package
echo ">=dev-lang/ruby-2.2.0" > /usr/portage/profiles/package.mask/myruby
and inserted the following line into my make.conf
RUBY_TARGETS="ruby21"
now it was possible to emerge ruby.
Is there a better way to solve this issue?
As far as I know, i will not need ruby for anything else (but i didn't thought that it is some how a dependency of geary either), so this solution is ok for me. So this thread could be marked as solved.
If I can assist someone to fix this bug, just tell me.