[freakboy3742]

Part 2 of the work started with beeware/briefcase-template#272.

Migrates the common project workflows to use Ruff, instead of flake8 and black.

Depends on the changes in beeware/briefcase#3144.

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

[mhsmith]

The app's pyproject.toml file doesn't contain any Ruff configuration. So checking out inputs.repository at the top level of the working directory, and then creating the app in a subdirectory of that, caused Ruff to use the configuration from inputs.repository rather than its defaults. Fixed by checking out inputs.repository into a separate subdirectory.