What would this add? Since the latest Swift release is installed on the github linux and I presume macOS runner images (though not on Windows), a linux/mac CI for a Swift package is as simple as running swift build or swift test.
It would be nice if there were a standard way to install the snapshot toolchains though, as the community efforts appear to have stalled, excepting maybe that new setup-swift one which still appears to have problems on Windows. Maybe that one or some others can be brought in-house and made the official way to install Swift toolchains when needed.