Double-check units on the "covariance is too big" warning

[dmcdougall]

[briadam]

The conditional logic for this warning https://github.com/libqueso/queso/blob/469911ac41a8a829b994ac296e341386589a0721/src/stats/src/TransformedScaledCovMatrixTKGroup.C#L330-L343 is comparing units of variance (covariance diagonal) to domain bounds. Should probably instead by comparing sqrt(var) to the bounds.