Fixes #2571. Wizards background shifts to gray when focusing, looks bad.

[BDisp]

Fixes

• Fixes Wizards background shifts to gray when focusing, looks bad. #2571

Proposed Changes/Todos

• Allowing containers to use the normal attribute instead of the focused color
• Adding unit test

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 I don't know why this is failing. All the test passed locally.