Fix Shift + letter behaviour in Press Keys

[xylix]

Currently there's some Run Keyword And Expect Errors in our Press Keys test that should be replaced with an actually passing test that succesfully inputs keys with shift. If this is not possible on macOS / some other platforms, we need to document this and if/else it somewhere.

Probably related to puppeteer/puppeteer#1313 . See
https://github.com/microsoft/playwright/blob/master/docs/api.md#class-keyboard
and
https://github.com/microsoft/playwright/blob/master/docs/api.md#pagepressselector-key-options

for more info.