Fix break

Author: David-Engel

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlDataReader.cs

@@ -4734,7 +4734,7 @@ public override Task<bool> ReadAsync(CancellationToken cancellationToken)
                 }
 
                 // Register first to catch any already expired tokens to be able to trigger cancellation event.
-                IDisposable registration = default;
+                CancellationTokenRegistration registration = default;
                 if (cancellationToken.CanBeCanceled)
                 {
                     registration = cancellationToken.Register(SqlCommand.s_cancelIgnoreFailure, _command);