CHANGELOG.md: entry added

Author: dconeybe

firebase-dataconnect/CHANGELOG.md

@@ -14,6 +14,8 @@
   ([#7909](https://github.com/firebase/firebase-android-sdk/pull/7909))
 - [changed] Internal change to use `SecureRandom` when generating operation IDs.
   ([#7910](https://github.com/firebase/firebase-android-sdk/pull/7910))
+- [changed] Internal refactor to use immutable byte arrays.
+  ([#NNNN](https://github.com/firebase/firebase-android-sdk/pull/NNNN))
 
 # 17.1.4