tkey: skip TKEY system test in FIPS mode

TKEY uses MD5 which is incompatible with FIPS.

bin/tests/system/tkey/prereq.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+. ../conf.sh
+
+$FEATURETEST --have-fips-mode && {
+	echo_i "TKEY is not compatible with FIPS mode." >&2
+	exit 255
+}
+exit 0