We use pre-existence of `rake_path` to decide whether we need to
regenerate dummy test gems in `tmp`. When changing rubies, the previous
implementation will believe that the correct `rake_path` exists
and avoids regenerating dummy gems, given an error like the following
when specs are run:
```
(...)
Could not find rubygems-generate_index lib directory in /path/to/rubygems/bundler/tmp/1/gems/base/ruby/3.2.0
# ./spec/support/builders.rb:253:in `block in update_repo'
# ./spec/support/helpers.rb:337:in `block in with_gem_path_as'
# ./spec/support/helpers.rb:351:in `without_env_side_effects'
# ./spec/support/helpers.rb:332:in `with_gem_path_as'
# ./spec/support/builders.rb:251:in `update_repo'
# ./spec/support/builders.rb:228:in `build_repo'
# ./spec/support/builders.rb:197:in `build_repo4'
# ./spec/commands/lock_spec.rb:103:in `block (2 levels) in <top (required)>'
(...)
```
To fix this, fix the part of the path that depends on the implementation
and the Ruby version so that we don't give false positives.
https://github.com/rubygems/rubygems/commit/fafacfa210