Test: Update tf-m-tests commit ID

Align with decoupling of config_impl.cmake.

Change-Id: I30a3d383db97f38c0a4ed61007472d095b0ec7f4
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/lib/ext/tf-m-tests/repo_config_default.cmake b/lib/ext/tf-m-tests/repo_config_default.cmake
index 7110be9..49b1440 100644
--- a/lib/ext/tf-m-tests/repo_config_default.cmake
+++ b/lib/ext/tf-m-tests/repo_config_default.cmake
@@ -10,5 +10,5 @@
 # Default configs of tf-m-tests repo
 
 set(TFM_TEST_REPO_PATH                  "DOWNLOAD"  CACHE PATH      "Path to TFM-TEST repo (or DOWNLOAD to fetch automatically")
-set(TFM_TEST_REPO_VERSION               "66e119aa"  CACHE STRING    "The version of tf-m-tests to use")
+set(TFM_TEST_REPO_VERSION               "21a4421d"  CACHE STRING    "The version of tf-m-tests to use")
 set(CMSIS_5_PATH                        "DOWNLOAD"  CACHE PATH      "Path to CMSIS_5 (or DOWNLOAD to fetch automatically")