Update adaptive_app's deps

[domesticmouse]

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 updates dependencies for the adaptive_app across all its codelab steps. The versions of flex_color_scheme and go_router have been bumped, with flex_color_scheme moving from a development pre-release to a stable version. The native iOS and macOS project files have been updated accordingly to reflect these dependency changes. Additionally, a redundant step for updating flex_color_scheme has been removed from the codelab_rebuild.yaml script, simplifying the build process. The changes are consistent and look correct. Good work!