chore(deps): update dependency dart to v3

Author: renovate[bot]

pubspec.yaml

@@ -4,7 +4,7 @@ version: 1.6.1
 homepage: https://github.com/FilledStacks/stacked/tree/master/packages/stacked_generator
 
 environment:
-  sdk: ">=2.17.0 <3.0.0"
+  sdk: "<4.0.0"
 
 dependencies:
   build: ^2.2.1