fix: finding stub app on macOS with . in formal name

[Mr-Sunglasses]

fix: #2151

• fix issue in finding stub app on macOS with . in formal name

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 PR!

You've got the general form of the solution correct - but there's a couple of housekeeping issues you need to take care of to get CI to pass. The most immediate problem is the lack of a changenote - you need to add a file that describes the change as it will appear in the release notes. Once you've fixed that, I suspect you'll hit two other problems:

• a code style issue picked up by black; and
• a test coverage failure. We have 100% branch coverage in our test suite; you're adding a fix for a bug here, so it should be accompanied by a test for that bug.

The Briefcase contribution guide describes the things you need to do as part of a PR, and how to set up your local environment to perform those checks.