fix for doxygen action

[rem1776]

Description
Updates the action to specify the older ubuntu image (see NOAA-GFDL#1664 for details). This is more of a short term fix, I will put in more updates eventually for the doxyfile to work with the latest doxygen versions.

How Has This Been Tested?
CI

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes