They cause flakies when different tests start them in parallel, and also
make the specs more complicated.

… command

rubygems/rubygems@9b9ba0bf1e

Since now every functionality that changes in Bundler 4 is under a
setting, we can enable that setting to test the new functionality,
without having to run our full CI twice.

This can actually be seen as increasing coverage, because Bundler 4
functionality will now be tested on Windows, MacOS, or any other
environment where previously "Bundler 4 mode" was not running.

rubygems/rubygems@1cb3e009fc

…for Bundler 5

rubygems/rubygems@b42b2e7055

After introducing the `simulate_version` setting, that's another call to
`Bundler#Settings#[]` that gets in the middle and makes these specs fail
when run in isolation.

rubygems/rubygems@722360e98e

…ll automatically after bundle gem

rubygems/rubygems@59ac0db26b

rubygems/rubygems@1413086e92

rubygems/rubygems@ab9b8c2511

rubygems/rubygems@91d7abe27f

rubygems/rubygems@f2826dafce

rubygems/rubygems@b16511598e

rubygems/rubygems@a2e4d8299f

rubygems/rubygems@53174e0aa6

ruby/json@3ae3eeb9d3