Add planned release date to 3.10 log entry

Change-Id: I35491be47146441438057c45803372d276a4885e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/459802
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Ivan Inozemtsev <iinozemtsev@google.com>

Author: iinozemtsev

CHANGELOG.md

@@ -29,7 +29,7 @@
 
 ## 3.10.0
 
-**Released on:** Unreleased
+**Released on:** 2025-11-12
 
 ### Language