Check whether the code can get correct spin-4 shear response de1/dg2 and de2/dg1

[mr-superonion]

Since I am not directly using that spin-4 part, I have not write an unit test to carefully check that part.

[mr-superonion]

this part of the code.

The current code uses 8 detection kernels to make sure there is no spin-4 leakage. Therefore, we do not need to include the spin-4 terms in the shear response.
If we use 4 detection kernels (there is spin-4 leakages), we need to include the spin-4 terms.