Use Task.CompletedTask (dotnet/extensions#2354)
Use Task.CompletedTask (dotnet/extensions#2354)

\n\nCommit migrated from https://github.com/dotnet/extensions/commit/69255c71b64b494f9d50b5aff0426b4969dfb009

aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore