try flutter versions

.github/workflows/dart.yml

@@ -16,7 +16,7 @@ jobs:
         name: Generate matrix from pubspec.yaml
         uses: flutter-actions/pubspec-matrix-action@v1
         with:
-          pubspec: "pubspec.yaml"
+          channel: "stable"
     outputs:
       matrix: ${{ steps.pubspec.outputs.matrix }}
 
@@ -36,6 +36,9 @@ jobs:
 
       - run: flutter --version
 
+      - run: dart pub add dev:lints
+      - run: dart pub add dev:test
+
       - name: Install dependencies
         run: flutter pub get
 

pubspec.yaml

@@ -3,12 +3,13 @@ description: the better router is a powerful, but for humans, flutter router.
 version: 2.1.0
 repository: https://github.com/dukex/better_router
 environment:
-  sdk: '>=2.17.5 <4.0.0'
+  sdk: ">=2.12.0"
+  flutter: ">=2.0.0"
 dependencies:
   flutter:
     sdk: flutter
 dev_dependencies:
-  lints: ^2.0.0
-  test: ^1.16.0
+  lints: any
+  test: any
   flutter_test:
     sdk: flutter