library/tests: replace md_psa.h with psa_util.h as include file for MD conversion

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index fe7a674..82b6bfc 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -14,7 +14,7 @@
 #include "mbedtls/platform.h"
 #include "mbedtls/constant_time.h"
 #include "mbedtls/oid.h"
-#include "md_psa.h"
+#include "mbedtls/psa_util.h"
 
 #include "ssl_misc.h"
 #include "ssl_tls13_keys.h"