fix build with gcc15 / c23

[nim65s]

fix:

gcc -g -Wall -Wwrite-strings -funroll-loops -Wstrict-prototypes -I. -Iinclude -fPIC -Ofast -DSVD_ACTIVATED=1 -DCTRLC=1  -DCOPYAMATRIX=1  -DLAPACK_LIB_FOUND -DUSE_LAPACK -c src/unit_test_util.c -o out/obj/unit_test_util.o
In file included from src/unit_test_util.c:36:
include/unit_test_util.h:55:17: error: 'bool' cannot be defined via 'typedef'
   55 |     typedef int bool;
      |                 ^~~~
include/unit_test_util.h:55:17: note: 'bool' is a keyword with '-std=c23' onwards
include/unit_test_util.h:55:5: warning: useless type name in empty declaration
   55 |     typedef int bool;
      |     ^~~~~~~