Add missing include

Fix build failures with config full

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/src/test_helpers/ssl_helpers.c b/tests/src/test_helpers/ssl_helpers.c
index d1e3d9c..e8bbc78 100644
--- a/tests/src/test_helpers/ssl_helpers.c
+++ b/tests/src/test_helpers/ssl_helpers.c
@@ -21,6 +21,7 @@
  */
 
 #include <test/ssl_helpers.h>
+#include "md_psa.h"
 
 #if defined(MBEDTLS_SSL_TLS_C)
 #if defined(MBEDTLS_SSL_HANDSHAKE_WITH_CERT_ENABLED)