swift

74be884c - [Concurrency] Use `warnUntilSwiftVersion(6)` in `safeToDropGlobalActor`.

[Concurrency] Use `warnUntilSwiftVersion(6)` in `safeToDropGlobalActor`. Now that there's only one call-site of `safeToDropGlobalActor`, it doesn't need to be exposed in the ActorIsolation header, and it doesn't need to avoid `warnUntilSwiftVersion` to match constraint system diagnostics. (cherry picked from commit 2fb14ce5ad8c9bfccf648750acb0f6c40d51b4ed)