Re-enable Intro to FlutterGPU on master (#2270)

This is a PR to track the state of `intro_flutter_gpu`. 

Blocked on: bdero/flutter_scene#48

## Pre-launch Checklist

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

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Effective Dart: Style]:
https://dart.dev/guides/language/effective-dart/style
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md

Author: domesticmouse

flutter_ci_script_beta.sh

@@ -25,7 +25,7 @@ declare -a CODELABS=(
   "haiku_generator"
   "homescreen_codelab"
   "in_app_purchases"
-  # TODO(domesticmouse): Add after beta is above Dart 3.7.0-0
+  # TODO(domesticmouse): Add after beta is above Dart 3.8.0-0
   # "intro_flutter_gpu"
   "namer"
   "next-gen-ui"

flutter_ci_script_master.sh

@@ -25,8 +25,7 @@ declare -a CODELABS=(
   "haiku_generator"
   "homescreen_codelab"
   "in_app_purchases"
-  # TODO(domesticmouse): Building assets for package:flutter_scene_importer failed.
-  # "intro_flutter_gpu"
+  "intro_flutter_gpu"
   "namer"
   "next-gen-ui"
   "testing_codelab"

flutter_ci_script_shared.sh

@@ -50,10 +50,10 @@ function ci_codelabs () {
 
                     # intro_flutter_gpu only runs with Impeller
                     if [ $CODELAB = 'intro_flutter_gpu' ]; then
-                        if [ $RUNNER_OS = 'macOS' ] || [ $RUNNER_OS = 'Windows' ]; then
-                            flutter config --enable-native-assets
-                            flutter build `echo $RUNNER_OS | tr '[:upper:]' '[:lower:]'` --debug
-                            flutter test --enable-impeller
+                        if [ $RUNNER_OS = 'macOS' ] || [ $RUNNER_OS = 'Linux' ]; then
+                        flutter config --enable-native-assets
+                        flutter build `echo $RUNNER_OS | tr '[:upper:]' '[:lower:]'` --debug
+                        flutter test --enable-impeller
                         else
                             echo "Skipping $CODELAB on $RUNNER_OS"
                         fi