freenull.c.head: include mlkem.h for MLKEM_{private,public}_key_free()

Author: tb

src/regress/lib/libcrypto/free/freenull.c.head

@@ -1,4 +1,4 @@
-/*	$OpenBSD: freenull.c.head,v 1.10 2024/08/30 05:00:38 tb Exp $	*/
+/*	$OpenBSD: freenull.c.head,v 1.11 2025/08/25 06:01:33 tb Exp $	*/
 
 #include <openssl/asn1.h>
 #include <openssl/cmac.h>
@@ -10,6 +10,7 @@
 #include <openssl/gost.h>
 #endif
 #include <openssl/hmac.h>
+#include <openssl/mlkem.h>
 #include <openssl/ocsp.h>
 #include <openssl/pkcs12.h>
 #include <openssl/ts.h>