Use latest version of SymPy

[yguclu]

Currently SymPDE requires sympy>=1.5,<=1.9. We should make the necessary changes in order to use newer versions of SymPy.

If we want to support Python 3.12, which does not ship with distutils anymore, it is necessary that we support sympy >= 1.12.

[EmilyBourne]

This is becoming more urgent as we get closer to Python 3.12 (to be released in October).

Although sympde does not encounter the warning itself, other packages (e.g. Pyccel) which are using sympy 1.6.2 in order to satisfy sympde dependencies, encounter the following warning:

../../../../.local/lib/python3.10/site-packages/sympy/external/importtools.py:4
  /home/scitas/.local/lib/python3.10/site-packages/sympy/external/importtools.py:4: DeprecationWarning: The distutils package is deprecated and slated for removal in Python 3.12. Use setuptools or check PEP 632 for potential alternatives
    from distutils.version import LooseVersion

Presumably when Python 3.12 becomes available (around October), it will be impossible to run Pyccel with this version while preserving a working installation of sympde.