gateware: fix pin assignments and remove deprecated `Case()`

[antoinevg]

This is failing the CI tests: https://github.com/greatscottgadgets/luna/actions/runs/8236675456/job/22523664217#step:5:32

This is building for me on amaranth==0.4.1 which should be equivalent to luna's amaranth~=0.4.0 but I'm probably the last person to ask about pip package resolution.

We're in a weird place, we need a stable pin for cynthion release but there's a lot of things in luna we need for urti and it would be nice to not have to rewrite them when amaranth>=0.5 comes out. 😛

[miek]

This is building for me on amaranth==0.4.1 which should be equivalent to luna's amaranth~=0.4.0 but I'm probably the last person to ask about pip package resolution.

Is that just building a design, or running the tests? That test fails locally for me with amaranth 0.4.1.

[antoinevg]

Argh okay, I only ran builds here.

[mndza]

Updated the tests.

[miek]

Thanks!