feat(flutter): update dependency flutter to >=3.16.0 (#208)

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

pubspec.yaml

@@ -6,7 +6,7 @@ homepage: https://github.com/zeshuaro/firestore_cache
 
 environment:
   sdk: ">=3.2.0 <4.0.0"
-  flutter: ">=3.13.9"
+  flutter: ">=3.16.0"
 
 dependencies:
   cloud_firestore: ^4.13.0