Test subspace basis involving a basis that uses the Piola transform

This currently triggers a compiler error, because the Python bindings try to create an interpolate method for functions that use std::array for values. That doesn't work because our current implementation transforms functions-to-be-interpolated onto the reference element using the (inverse) Piola transform. And that doesn't quite work for bool-valued functions.

This commit is deliberately short: Just the bare minimimum to trigger the problem. Once the problem is fixed we should add calls to the remaining tests here.