doc: release-notes: add a note about tests & samples

Mention the ztest api conversion and new tests expectations.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
diff --git a/doc/releases/release-notes-3.2.rst b/doc/releases/release-notes-3.2.rst
index ded2f56..b5f55f7 100644
--- a/doc/releases/release-notes-3.2.rst
+++ b/doc/releases/release-notes-3.2.rst
@@ -861,6 +861,10 @@
 Tests and Samples
 *****************
 
+* A large number of tests have been reworked to use the new ztest API, see
+  :ref:`test-framework` for more details. This should be used for newly
+  introduce tests as well.
+
 Issue Related Items
 *******************