require dart 3.1; update to the latest lints (#675)

Author: devoncarew

pkgs/file_testing/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.0.2
+
+* Require Dart 3.1.
+
 ## 3.0.1
 
 * Update the pubspec repository field to reflect the new package repository.

pkgs/file_testing/lib/file_testing.dart

@@ -3,4 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /// Matchers (from `package:test`) for use in tests that deal with file systems.
+library;
+
 export 'src/testing/core_matchers.dart';

pkgs/file_testing/pubspec.yaml

@@ -1,13 +1,13 @@
 name: file_testing
-version: 3.0.1
+version: 3.0.2
 description: Testing utilities for package:file.
 repository: https://github.com/dart-lang/tools/tree/main/pkgs/file_testing
 
 environment:
-  sdk: ^3.0.0
+  sdk: ^3.1.0
 
 dependencies:
   test: ^1.23.1
 
 dev_dependencies: 
-  lints: ^2.0.1
+  lints: ^5.0.0