Fix error in rtd.yaml

[aerorahul]

Description
Fixes an indentation error in readthedocs.yaml that was preventing the documentation to be built and deployed on RTD.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• pytests

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
• My changes need updates to the documentation. I have made corresponding changes to the documentation
• My changes generate no new warnings
• New and existing tests pass with my changes
• Any dependent changes have been merged and published

[WalterKolczynski-NOAA]

Builds now, API documentation is missing: https://wxflow--5.org.readthedocs.build/en/5/

[WalterKolczynski-NOAA]

API works now too. 🎊