Add a test job that opts-in SED fitting in OpenUniverse notebook

[troyraen]

I would think we could add a test job that opts in the SED fitting, but that should be separate from this PR.

Originally posted by @bsipocz in #347 (review)

This would require changing notebook param RUN_FITS to True and installing fsps and its dependencies (see nb pip-install cell). Installing fsps is currently problematic for python>=3.13 (see #347 (comment)).