If a platform specific variant would not match the current Ruby, we would still be
considering it compatible with the initial resolution and adding its
platform to the lockfile, but we would later fail to materialize it for
installation due to not really being compatible.

Fix is to only add platforms for variants that are also compatible with
current Ruby and RubyGems versions.

https://github.com/rubygems/rubygems/commit/75d1290843