Add new psa_key_agreement() to key exercises

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/tests/include/test/psa_exercise_key.h b/tests/include/test/psa_exercise_key.h
index f6be307..f44608b 100644
--- a/tests/include/test/psa_exercise_key.h
+++ b/tests/include/test/psa_exercise_key.h
@@ -138,7 +138,7 @@
     size_t capacity, int key_destroyable);
 
 /** Perform a key agreement using the given key pair against its public key
- * using psa_raw_key_agreement().
+ * using psa_raw_key_agreement() and psa_key_agreement().
  *
  * The result is discarded. The purpose of this function is to smoke-test a key.
  *