Update forecast.HRRR model name to match server update

[kahemker]

The HRRR CONUS 2.5km forecast model data name has changed.

• Closes HRRR CONUS 2.5km Forecast Model Name has changed #1291
• I am familiar with the contributing guidelines
• Tests added
• 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`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels and Milestone are assigned to the Pull Request and linked Issue.

• Tests are not added, but the existing test_forecast.py model() function now works for HRRR
• No API Changes
• No additional documentation. I just updated the name of the HRRR model forecast string
• I'm not sure exactly what I should do to the "what's new" file... sorry. Edit: Updated the appropriate "what's new" file

[wholmgren]

Thanks @kahemker. In the bug fixes section of this file you could add

* Fixed :py:class:`~pvlib.forecast.HRRR` by changing model name to reflect change on the server. (:issue:`1291`, :pull:`1292`)

[kahemker]

Just pushed another commit with the change to the "what's new" documentation. Let me know if I need to update anything else.

[wholmgren]

Thanks again @kahemker!