Improve multithreaded tests in UC Mode

[mdmintz]

Improve multithreaded tests in UC Mode

I found a few places where multithreading can be improved to prevent conflicts.

I'll have this update ready for the next release.

[mdmintz]

This was resolved in 4.17.12 - https://github.com/seleniumbase/SeleniumBase/releases/tag/v4.17.12