large_enums mir pass: fix is_enabled logic This logic got turned from a guard in `run_pass` to an `is_enabled` check in https://github.com/rust-lang/rust/pull/85158/changes/15d4728cda673e90b4db1ea2c60d18a6fae306d0#r2989096960, but that was done incorrectly. The pass must never be enabled without `unsound_mir_opts`!