Ubuntu 20.04 buildtools containers are EOL: https://github.com/dotnet/dotnet-buildtools-prereqs-docker/pull/1449 References to these images need to be upgraded to a supported version: * https://github.com/dotnet/diagnostics/blob/a083d65b84428784901cf8bacdf8403be18fa78f/eng/pipelines/pipeline-resources.yml#L89