i see, i believe this is because DispatchQoS and DispatchSpecificKey simply did not receive these conformances in Swift 6.0.1 on linux, which is yet another in a long list of platform traps between the macOS and linux versions of the standard library.
i understand GRDB.swift does not officially support linux, however, the 6.x release series was (serendipitously) buildable on linux, which allowed us to index the documentation for those tags on Swiftinit.
although you could probably restore linux buildability by adding #if-gated conformances or @preconcurrency imports, this really feels like something that needs to be fixed in the standard library itself.