Fix CI by pinning postcss version to 8.5.5 and disable app armor for browser tests (#2606) * Pin postcss version to 8.5.5 Not using 8.5.6 yet because it needs additional changes for type compatibility * disable app armor for browser tests See https://github.com/puppeteer/puppeteer/issues/12818 Ubuntu 23+ doesn't like running puppeteer without disabling AppArmor.