Update dependency dart to v3

Author: renovate[bot]

example/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: none
 version: 1.5.1
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '3.10.9'
 
 dependencies:
   disposebag: any

pubspec.yaml

@@ -6,7 +6,7 @@ repository: https://github.com/hoc081098/disposebag.git
 issue_tracker: https://github.com/hoc081098/disposebag/issues
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '3.10.9'
 
 dependencies:
   meta: ^1.7.0