fix: address ScrollController bug in MacosPopupButton

[GroovinChip]

Closes #297

This also addresses the failing tests.

Pre-launch Checklist

• [x] I have run dartfmt on all changed files
• [x] I have incremented the package version as appropriate and updated CHANGELOG.md with my changes
• [x] I have added/updated relevant documentation
• [x] I have run "optimize/organize imports" on all changed files
• [x] I have addressed all analyzer warnings as best I could

[github-actions[bot]]

Dart Code Metrics analyze report of macos_ui. ✅

Summary

• Scanned folders: lib

• Total scanned files: 72

• Total lines of source code: 8676

• Total classes: 178

• Average Cyclomatic Number per line of code: 0.25 / 6

• Average Source Lines of Code per method: 11

• Total tech debt: not found

• Found issues: 0 ✅

[whiplashoo]

LGTM! Dealing with ScrollControllers is never fun, right? 🙃