Add option "--no-screenshot" to prevent screenshots from getting saved at the end of tests

[mdmintz]

Add pytest option --no-screenshot to prevent screenshots from getting saved at the end of tests.

By default, screenshots are saved for every test failure.

[mdmintz]

Released in 4.7.1 - https://github.com/seleniumbase/SeleniumBase/releases/tag/v4.7.1