bump riscv cross compiler to gcc 13 + fix nits

tests/hello.c

@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <riscv-pk/encoding.h>
 #include "marchid.h"
+#include <stdint.h>
 
 int main(void) {
   uint64_t marchid = read_csr(marchid);