Add explanation for workaround in test code

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/tests/suites/test_suite_psa_crypto.function b/tests/suites/test_suite_psa_crypto.function
index 21de8a9..e1f90d2 100644
--- a/tests/suites/test_suite_psa_crypto.function
+++ b/tests/suites/test_suite_psa_crypto.function
@@ -4423,7 +4423,10 @@
     if( status != PSA_SUCCESS )
     {
         /* Invalid tag lengths are detected in CCM at this point, as they
-         * would be written into the first block. */
+         * would be written into the first block. They should really be
+         * detected in psa_aead_encrypt/decrypt_setup, and will be fixed
+         * to do so in the future, until that point, this is a
+         * workaround.*/
         TEST_EQUAL( status, expected_status );
         goto exit;
     }