[flutter_tools] bump min sdk version from 3.0.0-0 to 3.0.0 (#125158)

Allows use of APIs such as `Iterable.firstOrNull`.

Author: andrewkolos

packages/flutter_tools/pubspec.yaml

@@ -3,7 +3,7 @@ description: Tools for building Flutter applications
 homepage: https://flutter.dev
 
 environment:
-  sdk: '>=3.0.0-0 <4.0.0'
+  sdk: '>=3.0.0 <4.0.0'
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".