Update thermal solid input file

[chapman39]

Initially, it complains about having different polynomial interpolation orders between solid and heat transfer modules, but when I set them both to one, I get:

0: MFEM abort: SuperLUSolver: Found a singular matrix, U(210,210) is exactly zero!
0:  ... in function: void mfem::SuperLUSolver::HandleError(int) const
0:  ... in file: linalg/superlu.cpp:754

serac/data/input_files/tests/thermal_solid/thermal_expansion.lua

Line 36 in cc3e357

order = 1,