Fix build of unit test on 32b architecture

Fix build of unit test on 32b architecture

Fixes unittest build failure on i686 platform.

In file included from tests/isc/time_test.c:24:
tests/isc/time_test.c: In function ‘run_test_isc_time_formatISO8601TZms_test’:
tests/isc/time_test.c:284:32: error: passing argument 2 of ‘_assert_in_set’ from incompatible pointer type [-Wincompatible-pointer-types]
  284 |         assert_in_set(buf[23], plus_minus, sizeof(plus_minus));
      |                                ^~~~~~~~~~
      |                                |
      |                                size_t * {aka unsigned int *}
/usr/include/cmocka.h:2369:64: note: expected ‘const long long unsigned int *’ but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
 2369 |     const LargestIntegralType value, const LargestIntegralType values[],