Shouldn't impose Python upper bound

[EliahKagan]

palgoviz should permit installation on later versions of Python. The major and minor versions should be perhaps be given in environment.yml, but only the major version should be given in pyproject.toml, i.e., the ~ should be changed to ^. This will require testing and should probably be done at the same time as adding 3.12 support (#185), but it is conceptually its own issue. In particular, if the upper bound is changed to ~3.12 rather than ^3.12 to allow some dependency to be installed, that would not fix this issue.