Fix an unskip `GFSPhysicsDriver` translate test

[romanc]

Describe the bug

The translate test for GFSPhysicsDriver wasn't properly registered and thus the NDSL's translate test system automatically marked it as xfail (expected failure) because it couldn't find the translate test class. The behavior only started to show after some typing work in NDSL, which made things more strict.

In PR #65 we thus properly registered the translate test and once it was running, it failed in numerical validation. The translate test was thus properly skipped and show now be looked at, fixed and unskipped.

To Reproduce

Unskip the translate test for GFSPhysicsDriver. PR #65 contains a link here and instructions to unskip the test.

Expected behavior

We expect the translate test of GFSPhysicsDriver to run and pass.

Additional context

• tests: properly register and skip translate test for GFSPhysicsDriver #65
• ci: all the types (or at least most of them) enforced with mypy NDSL#258