Fixing PR incompatibility pileup.

[davidorme]

I merged some PRs too quickly

• Add docstrings to tests #104 required flake8 compliant tests and Update of water density and viscosity functions #100 included tests that didn't comply.
• Update of water density and viscosity functions #100 also added some constants that were not compliant with Python 3.11 requirements for non-mutable defaults in dataclasses, and Extend python versions covered to include Python 3.11 #102 added 3.11 testing.

End result - qa failure for the docstrings and then test failures on the 3.11 runners.

This PR:

• Fixes some flake8 non-compliant test docstrings.
• Fixes some Python 3.11 non-compliant dataclass field defaults.