[newlib-cygwin/cygwin-3_6-branch] Cygwin: add release note for primary group override fix

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=ac07897678d614bad085abb96dbf13ac87e07d93

commit ac07897678d614bad085abb96dbf13ac87e07d93
Author:     Corinna Vinschen <corinna@vinschen.de>
AuthorDate: Fri Dec 5 17:34:20 2025 +0100
Commit:     Corinna Vinschen <corinna@vinschen.de>
CommitDate: Mon Dec 22 12:37:23 2025 +0100

    Cygwin: add release note for primary group override fix
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
    (cherry picked from commit 0dd40232f268e02ddab301a6058a20dd8a512943)

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 bc778ba46f56..736ef8195f1e 100644
--- a/winsup/cygwin/release/3.6.6
+++ b/winsup/cygwin/release/3.6.6
@@ -24,3 +24,7 @@ Fixes:
   cmd.exe is started using rlwrap in Win11.
 
 - Fix a bug where app execution aliases no longer start correctly.
+
+- Fix primary group override for non-domain users and users of a
+  Microsoft account.
+  Addresses: https://cygwin.com/pipermail/cygwin/2025-December/259068.html