We were using a rack browser and testing the
`FeatureFlags::FeatureDisabled` exception was raised. However, we don't
test this exception in any other system tests; we only check it in
controller tests.
So we're using a real browser for consistency and because in Rails 7.1
this test is failing when enabling the new default option
`config.action_dispatch.show_exceptions = :rescuable` in the test
environment.
6288450ab4