Add audio_soloud back to CI

[domesticmouse]

The @experimental issue with audio_soloud should now be fixed.

Context: #2350

Pre-launch Checklist

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

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[gemini-code-assist]

Code Review

This pull request re-enables the audio_soloud codelab in the CI by uncommenting it in the CI script and updating the Dart SDK and flutter_soloud dependency versions across all steps of the codelab. The changes are straightforward and correctly implement the intended goal. I have one suggestion regarding dependency management to improve long-term maintainability by reducing duplication across the multiple pubspec.yaml files.