Bump sdk to ^3.9.0 (#2341)

## Pre-launch Checklist

- [x] I read the [Effective Dart: Style] _recently_, and have followed
its advice.
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- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

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Author: domesticmouse

animated-responsive-layout/step_03/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animated-responsive-layout/step_04/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animated-responsive-layout/step_05/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animated-responsive-layout/step_06/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animated-responsive-layout/step_07/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animated-responsive-layout/step_08/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animations/step_01/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animations/step_02_a/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animations/step_02_b/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter:

animations/step_02_c/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.1.0
 
 environment:
-  sdk: ^3.9.0-0
+  sdk: ^3.9.0
 
 dependencies:
   flutter: