Add coverage for code in doc/source/make_tables.py

[user27182]

Add a new doc test to be executed during the Build Documentation work flow to ensure there is coverage for some of the documentation source code. Specifically, tests are added for the make_tables.py module .

This does two things:

• Adds test coverage for the Dataset Gallery (see Add new Dataset Gallery docs page to summarize metadata for downloadable datasets #5822) rst generation from the dataset loaders. Currently, there are no tests checking the rst outputs.
• Since make_tables loads all datasets from downloads.py, this should eliminate the need to use codecov skips for that module, and give a more accurate representation of the actual test coverage

[user27182]

pre-commit.ci autofix

[codecov]

Codecov Report

Attention: Patch coverage is 99.45652% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 96.23%. Comparing base (f9d2d86) to head (e953729).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5921      +/-   ##
==========================================
- Coverage   96.83%   96.23%   -0.61%     
==========================================
  Files         139      139              
  Lines       24039    24498     +459     
==========================================
+ Hits        23279    23575     +296     
- Misses        760      923     +163