Add changelog entry for closing real-time background connections.

Author: tusharkhandelwal8

firebase-config/CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
-
+[fixed] Fixed an issue where the connection to the real-time Remote Config backend could remain
+open in the background.
 
 # 22.1.0
 * [feature] Added support for custom signal targeting in Remote Config. Use `setCustomSignals` API for setting custom signals and use them to build custom targeting conditions in Remote Config.