[newlib-cygwin/cygwin-3_6-branch] Cygwin: Update release note for 3.6.6

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=c6680700f8d37effd928698fa818ffc4a927df42

commit c6680700f8d37effd928698fa818ffc4a927df42
Author: Takashi Yano <[email protected]>
Date:   Thu Jan 8 21:18:06 2026 +0900

    Cygwin: Update release note for 3.6.6

Diff:
---
 winsup/cygwin/release/3.6.6 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/winsup/cygwin/release/3.6.6 b/winsup/cygwin/release/3.6.6
index 736ef8195..192bfd2c9 100644
--- a/winsup/cygwin/release/3.6.6
+++ b/winsup/cygwin/release/3.6.6
@@ -28,3 +28,7 @@ Fixes:
 - Fix primary group override for non-domain users and users of a
   Microsoft account.
   Addresses: https://cygwin.com/pipermail/cygwin/2025-December/259068.html
+
+- Fix the deadlock between the parent and child processes, where both lock
+  the same file and attempt to close it simultaneously.
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-December/259187.html