Update CHANGELOG.md for Auth (#4465)

Author: renkelvin

Firebase/Auth/CHANGELOG.md

@@ -1,3 +1,7 @@
+# v6.4.1
+- [fixed] Added support of UISceneDelegate for URL redirect. (#4380)
+- [fixed] Fixed rawNonce in encoder. (#4337)
+
 # v6.4.0
 - [feature] Added support for Sign-in with Apple. (#4183)