Unpin rdkit on mypy

[IAlibay]

Opening up this PR so we remember to do this.

@mikemhenry I believe you put the pin in, do you know if there's an issue upstream to work out why this duplicate self is happening?

[mikemhenry]

Yes the error was that there was a syntax error with the rdkit typing stubs and that pinned version fixed it, I can try and fix that on #733

[mikemhenry]

This is the mypy error: /home/runner/micromamba/envs/openfe_env/lib/python3.11/site-packages/rdkit-stubs/Chem/rdMolDescriptors.pyi:247: error: Duplicate argument "self" in function definition seen with rdkit 2024.03.2 py311h1d78c4b_0 conda-forge

I will see if 2023.09.5 works but with python relaxed (it was pined to 3.9 which was causing the issues with the env solving).

[mikemhenry]

Also see rdkit/rdkit#7401