Do not paste text on macOS in e2e tests

Created by: mrnugget

Pasting text was introduced in f2365a5f3e8b729663d83f1158d6d4ccabb28903 and doesn't work on my macOS machine.

Reading through https://github.com/GoogleChrome/puppeteer/issues/1313 (and a ton of other GitHub issues and SO questions/answers) tells me that other people also couldn't get pasting via Meta+V to work on macOS with Puppeteer.

This commit adds an override for macOS while leaving the existing paste function as is.