Update Firestore Changelog for 10.3.0 (#10544)

Author: ehsannas

Firestore/CHANGELOG.md

@@ -1,8 +1,7 @@
-# Unreleased
-- [fixed] Fix App crashed when there are nested data structures inside IN Filter.
-
 # 10.3.0
 - [feature] Add MultiDb support.
+- [fixed] Fix App crashed when there are nested data structures inside IN
+  Filter (#10507).
 
 # 10.2.0
 - [fixed] Fix FAILED_PRECONDITION when writing to a deleted document in a