doc: release: Add a release entry

Add `__deprecated_version` macro to the Toolchain entry list.

Signed-off-by: James Roy <rruuaanng@outlook.com>
diff --git a/doc/releases/release-notes-4.3.rst b/doc/releases/release-notes-4.3.rst
index 82b11b8..906002f 100644
--- a/doc/releases/release-notes-4.3.rst
+++ b/doc/releases/release-notes-4.3.rst
@@ -272,6 +272,10 @@
 
   * :kconfig:option:`CONFIG_TASK_WDT_DUMMY`
 
+* Toolchain
+
+  * :c:macro:`__deprecated_version`
+
 .. zephyr-keep-sorted-stop
 
 New Boards