updates serpent tools dependency and pins python version

[samgdotson]

Summary of changes

This PR updates the environment.yml file by

• pinning a version of Python that is less than 3.12
• installing serpentTools via pip directly from GitHub, rather than PyPI.

This should fix the failing tests on GH actions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Required for Merging

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• My change is a source code change
  • I have added/modified tests to cover my changes
  • I have explained why my change does not require new/modified tests
• My change is a user-facing change
  • I have recorded my changes in the changelog for the upcoming release
• My change is exclusively related to the repository (e.g. GitHub actions workflows, PR/issue templates, etc.)
  • I have verified or justified that my change will work as intended.
• All new and existing tests passed.
  • CI tests pass
  • Local tests pass (including Serpent2 integration tests)

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• Issue: #

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[samgdotson]

@yardasol I did my best to move the needle on this... I'm not sure what testing you've done but I'm sure you're aware of the Numpy issues. I worked on it for a bit but it feels a little like whack-a-mole.

Fortunately, the error message is different. I now suspect the problem is with the installation of saltproc itself. I'm not totally sure how to tell setuptools to install a package from GitHub... I found this old documentation (which is a bit light on the documentation) suggesting something called "dependency links". But I'm not sure how much hacking you want to do with setuptools since I think it's becoming deprecated, anyway.

[yardasol]

Thanks @samgdotson , I suspect a better solution would be to move away from setuptools to a more modern build procedure, like a pyproject.toml