test-sizeof: add pid_t and gid_t

C.f. #6975.

src/test/test-sizeof.c

@@ -60,6 +60,8 @@ int main(void) {
         info(time_t);
         info(usec_t);
         info(__time_t);
+        info(pid_t);
+        info(gid_t);
 
         info(enum Enum);
         info(enum BigEnum);