Testing: Run with `--shuffle` flag to capture implicit dependencies

[madsmtm]

I've just now found out that the test_class test in runtime/mod.rs on GNUStep is somehow dependent on other things running before it, though yet unsure what.

Really troublesome to figure out given that testing it means I gotta go through CI.

[madsmtm]

Example run: https://github.com/madsmtm/objc2/actions/runs/5306116792/jobs/9603493154