doc: release: Add a release entry

Add `__deprecated_version` macro to the Toolchain entry list.

Signed-off-by: James Roy <[email protected]>

Author: rruuaanng

doc/releases/release-notes-4.3.rst

@@ -257,6 +257,10 @@ New APIs and options
 
   * :c:func:`sys_count_bits`
 
+* Toolchain
+
+  * :c:macro:`__deprecated_version`
+
 * Task Watchdog
 
   * :kconfig:option:`CONFIG_TASK_WDT_DUMMY`