Setting fitting parameters and `symCheck()`

[phockett]

New bug, trying to run a fit currently results in "RecursionError: maximum recursion depth exceeded while calling a Python object".

Upon inspection, this was due to the use of .drop(inplace=True) in symCheck(), which was not working and resulting in all fitting params being reset, with vary=False (reference case should be as shown at https://pemtk.readthedocs.io/en/latest/fitting/PEMtk_fitting_demo_multi-fit_tests_130621-para_010922.html#Setup)

This is now changed to .pop() in 5df6a0e, which seems to work as expected. This may be Pandas and/or Python version specific - tested OK with PD 1.4.1, Python 3.9.10.

TODO:

• test other versions.
• check Docker builds, why is PD 1.4.1 installed, possibly Xarray dependency? May need to added explicit conda pd install line to pull newer versions.