Build : Update tf-m-tests repo version

Update tf-m-tests repo version to db53c6b.

Change-Id: I17eca6d0ee19ab103cefc74a85034614b4735e29
Signed-off-by: Feder Liang <Feder.Liang@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 83df1f2..c343bbd 100644
--- a/lib/ext/tf-m-tests/repo_config_default.cmake
+++ b/lib/ext/tf-m-tests/repo_config_default.cmake
@@ -8,5 +8,5 @@
 # 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               "f6b208d"   CACHE STRING    "The version of tf-m-tests to use")
+set(TFM_TEST_REPO_VERSION               "db53c6b"   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")