fix(deps): update dependency cloud_firestore to ^4.15.6 (#343)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

pubspec.yaml

@@ -9,7 +9,7 @@ environment:
   flutter: ">=3.19.2"
 
 dependencies:
-  cloud_firestore: ^4.15.5
+  cloud_firestore: ^4.15.6
   flutter:
     sdk: flutter
   shared_preferences: ^2.2.2