tests: do not test on MacOS 10.15 any more (#16465)
tests: do not test on MacOS 10.15 any more (#16465)

Playwright v1.25 was the last release to support macOS 10.15, so we
no longer need to test on macOS 10.15.
microsoft/playwright,microsoft/playwright,microsoft/playwright,microsoft/playwright,microsoft/playwright,microsoft/playwright,microsoft/playwright,microsoft/playwright,microsoft/playwright