security/py-python-nss: Fix build with Python 3.12

src/py_nspr_error.c:189:23: error: too few arguments provided to function-like macro invocation

189 |         va_start(vargs);
    |                       ^

/usr/include/sys/_stdarg.h:41:9: note: macro 'va_start' defined here

41 | #define va_start(ap, last)      __builtin_va_start((ap), (last))
   |         ^

Reported by: pkg-fallout