Update Xenial build image on Netlify

[elzannewentzel]

The Ubuntu Xenial build image for the about and learn platforms need to be updated before 15 November 2022. Build will fail after this date because Netllify will not support Xenial anymore: https://answers.netlify.com/t/please-read-end-of-support-for-xenial-build-image-everything-you-need-to-know/68239