Warnings in tests

[DanielAndreasen]

I get two warnings when running the tests, and this is how I fixed them:

• Any delim_whitespace=True should be replaced with sep=r"\s+" when reading csvs with pandas
• ~https://github.com/BrownDwarf/gollum/blob/main/src/gollum/precomputed_spectrum.py#L181 should be replaced with shifted_spec.set_radial_velocity_to = rv * u.km / u.s to avoid the deprecation warning.~ Note: This fix does not work! It will break the code. Maybe this part should be better tested. With this wrong fix, this tutorial does not work: https://gollum-astro.readthedocs.io/en/latest/tutorials/best_fit_for_fixed_template.html

All other tests now runs without errors for me.

Review link: https://github.com/openjournals/joss-reviews/issues/6601

[Sujay-Shankar]

The most recent commit should have fixed both of these changes. The radial velocity method is actually a little deceptive, as it just seems to be an in-place setter method but doesn't actually change the spectral axis, which is what gollum wants. We actually want to use shift_spectrum_to(radial_velocity=rv*u.km/u/s) and this does the desired behavior of shifting the spectral axis. The tutorial should now work with this change.