PR #59 build is failing:
##[warning]An image label with the label Ubuntu 18.04 does not exist.
From https://techcommunity.microsoft.com/t5/linux-and-open-source-blog/canonical-ubuntu-18-04-lts-reaching-end-of-standard-support/ba-p/3822623
On 31 May 2023, Ubuntu 18.04 LTS will reach the end of standard support.
The article recommends upgrading to v20.04 LTS or v22.04. I'll experiment with updating the Azure pipeline YAML.