Fix SPM integration of the latest version of swift-testing

[fortmarek]

Short description 📝

Fixes latest version of swift-testing. The latest version due to the addition of these Swift flags that we were not properly escaping and they were treated as separate options.

I removed SwiftLint from the app_with_spm_dependencies fixture since we were not really using it and since swift-lint has an exact dependency on swift-syntax that's different from swift-testing, it's currently impossible to have both libraries in your Package.swift (if you want to have the latest version of swift-testing and don't want to fork SwiftLint)

How to test the changes locally 🧐

Testing AppKit in app_with_spm_dependencies should work.

Contributor checklist ✅

• The code has been linted using run mise run lint:fix
• The change is tested via unit testing or acceptance testing, or both
• The title of the PR is formulated in a way that is usable as a changelog entry
• In case the PR introduces changes that affect users, the documentation has been updated

Reviewer checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase
• Reviewer has checked that, if needed, the PR includes the label changelog:added, changelog:fixed, or changelog:changed, and the title is usable as a changelog entry