updating change log

updating change log wrt #9134

Author: eldhosembabu

FirebaseInAppMessaging/CHANGELOG.md

@@ -1,3 +1,6 @@
+# 2022-01 -- v8.12.0
+- [fixed] In-App Messaging's test message does not include appData in response (#9126).
+
 # 2021-12 -- v8.11.0
 - [fixed] InApp message is shown every new session (#8907).
 - [fixed] Duplicate messages can occur when two campaigns are triggered by different events in In-App Messaging (#9070).