Use Pandas 2.0

Created by: Zaharid

I tried updating to pandas 2.0. So far I have seen an error here:

https://github.com/NNPDF/nnpdf/blob/b5ee4ba61b25e596b3403326f9fb1ef5e861d071/validphys2/src/validphys/tableloader.py#L84

Prescient docstring.

    def set_actual_column_level0(df, new_levels):
        """Set the first level of the index to new_levels. Note:
        This is a separate function mostly because it breaks
        in every patch update of pandas."""
        cols = df.columns
>       cols.set_levels(new_levels, inplace=True, level=0)
E       TypeError: MultiIndex.set_levels() got an unexpected keyword argument 'inplace'