Fixes #2830. v1 Allow use LangVersion 9.0 on the UICatalog project.

[BDisp]

Fixes #2830- More agile advanced language feature for the UICatalog scenarios.

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[BDisp]

@tig do you know why the checks aren't executing on the v1_develop branch? It say:

Some checks haven’t completed yet
1 expected check