Playwright tests fail in Windows and Mac

[planger]

https://github.com/marcdumais-work/theia/actions/runs/4679291140

Windows and macOS have failed: Windows has an issue with the way THEIA_CONFIG_DIR is set in playwright package.json. On Mac, there's a failure in theia-text-editor.test.ts, but the new tests have passed. So, I think this PR does not make things worse - if we want to run these tests on the other OS, there will be a bit of work, not directly related to this contribution.

Originally posted by @marcdumais-work in #12381 (comment)

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Failure on Windows:

Failures on macOS (1/2 passed during retry):

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Here's how to quickly modify the Playwright workflow so it runs on all OS, when pushed on a branch (adjust the branch name, from "playwright-add-terminal", so it matches your test branch):