Add version number debug check to the GnuTLS interop test as well

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 0548c14..2fe7a40 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -9702,6 +9702,7 @@
             -c "<= parse certificate verify"          \
             -c "mbedtls_ssl_tls13_process_certificate_verify() returned 0" \
             -c "<= parse finished message" \
+            -c "Protocol is TLSv1.3" \
             -c "HTTP/1.0 200 OK"
 
 requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3