Cygwin: add release msg for mq_unlink changes

Signed-off-by: Corinna Vinschen <[email protected]>
(cherry picked from commit df63cbf)

Author: github-cygwin

winsup/cygwin/release/3.5.6

@@ -19,3 +19,6 @@ Fixes:
 
 - Minor updates to load average calculations.
   Addresses: https://cygwin.com/pipermail/cygwin/2024-August/256361.html
+
+- Fix mq_unlink().
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-January/257119.html