RBI gem generation test is failing on CI but not locally

[egiurleo]

The test "must not include rbi definitions into tapioca RBI" is failing on CI, but passes locally.

Here's an example of the CI failure.

It only fails on Ruby 3.3 and Rails current (7.1), and fails whether it is run on its own or with other tests, and also regardless of the order in which tests are run.

I skipped this test in #2021 because it is blocking the release of other fixes to CI, but we should revisit it soon.

[egiurleo]

@Morriar suggests looking at this PR: https://github.com/Shopify/tapioca/pull/1949