test/snippets: fix time.c compiler error on 32-bit arches

[enr0n]

Cast t to unsigned long and use the %lu format specifier instead of %zd. This is more portable to 32-bit arches, avoiding the following compiler error:

snippets/time.c:2:31: error: format ‘%zd’ expects argument of type ‘signed size_t’, but argument 3 has type ‘time_t’ {aka ‘long int’} [-Werror=format=] 2	printf("[%s] time() yielded %zd\n", where, t);	~~^ ~
int time_t {aka long int}
%ld

cc1: all warnings being treated as errors

[wolfcw]

nice catch, thanks!