Fix possible memory overrun in tests

[bandi13]

Found by one of our other tests:

In file included from wolfcrypt/test/test.c:43:
wolfcrypt/test/test.c: In function ‘certext_test’:
./wolfssl/wolfcrypt/types.h:722:39: error: ‘__builtin_memcmp_eq’ specified bound 32 exceeds source size 21 [-Werror=stringop-overread]
  722 |             #define XMEMCMP(s1,s2,n)  memcmp((s1),(s2),(n))
      |                                       ^~~~~~~~~~~~~~~~~~~~~
wolfcrypt/test/test.c:18504:9: note: in expansion of macro ‘XMEMCMP’
18504 |     if (XMEMCMP(skid_rsa, cert.extSubjKeyId, sizeof(cert.extSubjKeyId)))
      |         ^~~~~~~
wolfcrypt/test/test.c:18456:10: note: source object declared here
18456 |     byte skid_rsa[]   = "\x33\xD8\x45\x66\xD7\x68\x87\x18\x7E\x54"
      |          ^~~~~~~~

[bandi13]

retest this please. Issue in generic-config-parser: --enable-ed448 --enable-opensslextra unable to get a cert.