Don't run CI builds on TruffleRuby and Rails 5.0, 5.1, and 5.2

[andrykonchin]

The latest TruffleRuby release (22.2.0) is compatible with CRuby 3.0 so now they will be check on CI against the same Rails versions.

TruffleRuby CI builds fail on Rails 5.0, 5.1 and 5.0 because of missing rb_check_safe_obj function. It was removed in CRuby 3.0 (https://github.com/ruby/ruby/commit/ada2f71c70bb11f1d71485e2090ce36872608217)