For quite a while already we use ReadyRoll.MSBuild NuGet package. Event that ReadyRoll is not ReadyRoll anymore, it is still being regularly updated and keeps working with most recent SCA addins. It contains same build extensions, and works flawlessly on our build agents without need to install anything. Biggest problem is absence of nuget support in .sqlproj files, which makes adding/updating packages bit tricky: https://documentation.red-gate.com/rr1/installing/build-components
SQL Change Automation documentation doesn't contain this section, so it's hard to say for sure how long will it stay the way it is.
For the sake of completeness, properties to add to your .sqlproj as of today:
<ReadyRollNuGetBaseFolder>$(MSBuildThisFileDirectory)..\packages</ReadyRollNuGetBaseFolder>
<ReadyRollNuGetIsRestored Condition="$([System.IO.Directory]::GetDirectories($(ReadyRollNuGetBaseFolder), 'ReadyRoll.MSBuild.*').Length) != 0">True</ReadyRollNuGetIsRestored>
<SqlChangeAutomationTargetsPath Condition="$(ReadyRollNuGetIsRestored) == 'True'">$([System.IO.Directory]::GetDirectories($(ReadyRollNuGetBaseFolder), 'ReadyRoll.MSBuild.*')[0])\tools\ReadyRoll.Data.Schema.SSDT.targets</SqlChangeAutomationTargetsPath>