Build: Add version.txt to track tf-m-tests version

Although auto-downloading tf-m-tests repo by CMake has been removed for
split build, it is still worth to track the recommended tf-m-tests
version in TF-M.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: Ic9873da01d01bfde6a5a1bf71b2758a109594e46
diff --git a/lib/ext/tf-m-tests/version.txt b/lib/ext/tf-m-tests/version.txt
new file mode 100644
index 0000000..e313a01
--- /dev/null
+++ b/lib/ext/tf-m-tests/version.txt
@@ -0,0 +1,11 @@
+#-------------------------------------------------------
+# Copyright (c) 2023, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#-------------------------------------------------------
+
+# This file tracks the recommended tf-m-tests version to verify TF-M.
+# Developers should keep the version value up to date to make sure it fits current TF-M version.
+# TF-M does not rely on this file to build.
+
+version=7723011