Update comment

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/tests/scripts/depends.py b/tests/scripts/depends.py
index d1de526..3547f42 100755
--- a/tests/scripts/depends.py
+++ b/tests/scripts/depends.py
@@ -529,7 +529,8 @@
             # Cipher key types
             'cipher_id': ExclusiveDomain(cipher_key_types, build_and_test),
 
-            # XTS is not supported via the PSA API.
+            # XTS is not yet supported via the PSA API.
+            # See https://github.com/Mbed-TLS/mbedtls/issues/6384
             'cipher_chaining': ExclusiveDomain(cipher_chaining_symbols,
                                                build_and_test,
                                                exclude=r'PSA_WANT_ALG_XTS'),