Update CHANGES.txt for 3.19.3

The 3.19.2 release was supposed to fix the missing Python 3.10 wheel for
Windows, but this turned out to need some more fixes. This commit
updates CHANGES.txt to reflect that this fix will happen in 3.19.3
instead of 3.19.2.

Author: acozzette

CHANGES.txt

@@ -1,8 +1,10 @@
-2022-01-05 version 3.19.2 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+2022-01-10 version 3.19.3 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
 
   Python
   * Fix missing Windows wheel for Python 3.10 on PyPI
 
+2022-01-05 version 3.19.2 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
   Java
   * Improve performance characteristics of UnknownFieldSet parsing (#9371)