check out submodules in ci

[dougchansan]

c876e2b added tomlc17 as a submodule, but ci checks out without submodules, so every job stops at configure with tomlc17 submodule is missing. this fetches them in both jobs.

[dougchansan]

@siahisaforker with submodules fetched, the remaining red jobs (here and on #35 / #37) are all tests/modern_memory_service_test.c, which is already failing on main:

• msvc: __asm__("func_...") labels don't compile
• macos: the labels miss the _ symbol prefix, so it fails to link
• windows mingw: segfaults at runtime (reproduces locally with clang too). probably the 28-byte MGNativeExit return not matching the win64 abi

it's only the moderngekko runtime path, so i've left it alone.

[siahisaforker]

should be good to go, thanks