It failed because it couldn't find immutable collections, ASF doesn't have it either, it doesn't look like it's needed to satisfy the compiler anymore (SK2 includes it through protobuf-net)
Closes#2316
The issue we're facing right now comes from the fact of desynchronization of packages between different projects. Since I didn't find any way to "fix" the package versions of our plugins to the main ASF project, we'll instead use centralized Directory.packages.props which specifies appropriate versions