Out-of-date instruction to use run-playwright-tests

[jyasskin]

https://modern-web.dev/docs/test-runner/browser-launchers/playwright/ says to use https://github.com/marketplace/actions/run-playwright-tests, but that page says it's deprecated and to use npx playwright install --with-deps instead.

[Westbrook]

We'd be happy to accept a PR with these updated instructions! 🙏🏼