Add comment regarding the wire-version used in TLS 1.3 records

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 554e7b8..2e09907 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -3996,6 +3996,8 @@
 
     ASSERT_ALLOC( buf, ciphertext->len );
     rec.type   = MBEDTLS_SSL_MSG_APPLICATION_DATA;
+
+    /* TLS 1.3 uses the version identifier from TLS 1.2 on the wire. */
     mbedtls_ssl_write_version( MBEDTLS_SSL_MAJOR_VERSION_3,
                                MBEDTLS_SSL_MINOR_VERSION_3,
                                MBEDTLS_SSL_TRANSPORT_STREAM,