fix typo on calcparams_desoto help

[EduardoSarquis]

There's a typo in the documentation of the "saturation_current" parameter on line 1553.

• Closes Typo at pvlib.pvsystem.calcparams_desoto #2163
• I am familiar with the contributing guidelines
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

As part of the PVLib workshop at the PVPMC Workshop on Copenhagen, I learned how to contribute to PVLib with an simple example of fixing a typo.

[EduardoSarquis]

The contribution can be found here.

[kandersolar]

LGTM, thanks @EduardoSarquis !