SymPy 1.10 is broken

The Latest Sympy master is at the moment not supported by pystencils. Problems occur with deepcopy. An example of failure is shown here: https://i10git.cs.fau.de/holzer/pystencils/-/jobs/658250.

The problem was introduced with this commit to SymPy: https://github.com/sympy/sympy/commit/ef0de0c80ab13501076d9bf611a111250bbc88b0