ci: run fake ship tests under gc

[matthew-levan]

Adds --gc to the boot phase of the fake ship tests as the binary we build for them already uses the correct copts.

Resolves #332.

[barter-simsum]

When I tried to boot an existing pier with the full debug binary, it just printed a bunch of hex addresses and eventually a "boot failed". Is this normal behavior?

No. --config=dbg only optimizes at -O0 and turns on c3_dessert debug asserts.

[barter-simsum]

@matthew-levan can you confirm this behavior? This might be expected if the pier was built with U3_MEMORY_DEBUG or U3_CPU_DEBUG and you tried running on a binary without those options. Or if you passed those options when trying to rerun the pier and it wasn't built with those options. But this isn't at all expected for just --config=dbg

--config=dbg isn't a full debug configuration and we shouldn't be running it in ci because the unoptimized binary is quite a bit slower.

[matthew-levan]

Ok, so to recap: we just needed to add --gc to the boot phase of the fake ship tests.

[barter-simsum]

lftm. approved