Fix compiler tests with zig 0.12/0.13/0.14

[mkannwischer]

#15 identified that current slhdsa-c tests fail when compiling with zig in CI (aarch64 + x86, all tested versions - 0.12/0.13/0.14) which is odd. The zig tests got disabled for now.

You can see the failures here: https://github.com/pq-code-package/slhdsa-c/actions/runs/16287258520/job/45989873133

=== test summary ===
PASS: 1190
FAIL: 58
make: *** [Makefile:39: test] Error 1

One should be able to reproduce by:

nix develop .#ci_zig0_14
make test

but that does not result in any errors for me on both AArch64 MacOS and x86 Linux. Maybe this was just a glitch?