[Auth] Update CHANGELOG.md for #14011 (#14076)

Author: ncooke3

FirebaseAuth/CHANGELOG.md

@@ -1,7 +1,8 @@
-# Unreleased
+# 11.5.0
 - [fixed] Restore pre-Firebase 11 decoding behavior to prevent users getting
   logged out when upgrading from Firebase 8.10.0 or earlier to Firebase 11.
-  (#14011)
+  Note that this fix will not be in the 11.5.0 zip and Carthage
+  distributions, but will be included from 11.6.0 onwards. (#14011)
 
 # 11.4.0
 - [fixed] Restore Firebase 10 behavior by ignoring `nil` display names used