This is a regression from https://github.com/rubygems/rubygems/commit/cf749f8ffabd. The
funny thing is that we have a spec for this feature, so it was unclear
how we regressed here. It turns out there was a bug in one of our
negative matchers checking that gems ARE NOT included in a bundle.

This commit fixes the bug in the negative matcher and reverts
https://github.com/rubygems/rubygems/commit/cf749f8ffabd (with a slightly simpler diff).

https://github.com/rubygems/rubygems/commit/3f9a4ff32a