ci: configure with -DCMAKE_SYSTEM_NAME=Haiku for Haiku

Fixes ci regression introduced in e8b69b03fe7dc4b0f1102e9e07acaf87498f3222

.github/workflows/create-test-plan.py

@@ -653,6 +653,7 @@ def spec_to_job(spec: JobSpec, key: str, trackmem_symbol_names: bool) -> JobDeta
             job.cmake_arguments.extend((
                 f"-DCMAKE_C_COMPILER={job.cc}",
                 f"-DCMAKE_CXX_COMPILER={job.cxx}",
+                "-DCMAKE_SYSTEM_NAME=Haiku",
                 "-DSDL_UNIX_CONSOLE_BUILD=ON",
             ))
             job.shared_lib = SharedLibType.SO_0