Update window.py to be able to create dialogs in Textual

[Codep3]

When trying to create a dialog using the Textual backend, I get a TypeError warning about too many inputs
The code used works on GTK.
This change solves that error

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

Thanks for the fix. Not sure where that bug leaked in, but this definitely fixes it!

As a minor adminstrative thing, I've added the changenote file that was causing CI to fail - if you're getting into Toga contribution, it would be worth reading through our contribution guide. That document contains lots of details about how to set up to test your code, and other requirements that we have related to submissions to the project.

[Codep3]

Thank you for the help getting it merged!
If I find anything else I can contribute to, I'll go through the guide and set up the dev environment, thanks!