I've been trying out the new 6.0 and 6.1 Musl SDKs to build some packages and they work great. However, the lack of XCTest means I cannot run the tests for these packages against Musl, as [the build of the Musl SDK stops with swift-corelibs-foundation](https://github.com/swiftlang/swift-docker/blob/main/swift-ci/sdks/static-linux/scripts/build.sh#L685). @al45tair, any reason XCTest can't be included also? It would be great if I can run the tests.