firebase-dataconnect/CHANGELOG.md: update PR number in change log entry.

Author: dconeybe

firebase-dataconnect/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Unreleased
 * [changed] Changed gRPC proto package to v1 (was v1beta).
-  ([#NNNN](https://github.com/firebase/firebase-android-sdk/pull/NNNN))
+  ([#6729](https://github.com/firebase/firebase-android-sdk/pull/6729))
 
 # 16.0.0-beta04
 * [changed] `FirebaseDataConnect.logLevel` type changed from `LogLevel` to