Improve test_docs pre-check with Intersphinx URLs

[lola831]

Description

This PR changes our pre-check for running tests/test_docs.py so that instead of just trying to connect to docs.python.org we now iterate through all configured Intersphinx URLs. Previously, CI would fail fairly often when one of these external inventories timed out during the Sphinx build, even though the pre-check had passed.

Issue Link

N/A

Checklist

• I have tested the changes locally via pytest and/or other means
• I have added or updated relevant documentation
• I have autoformatted the code with black and isort
• I have added test cases (if applicable)

Additional Notes

N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.99%. Comparing base (20292f3) to head (356686a).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #419      +/-   ##
==========================================
+ Coverage   89.89%   89.99%   +0.09%     
==========================================
  Files          54       54              
  Lines       13551    13580      +29     
==========================================
+ Hits        12182    12221      +39     
+ Misses       1369     1359      -10     

see 10 files with indirect coverage changes

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[dfremont]

Looks good, just nitpicks.

[lola831]

@dfremont I restored the explanatory note and reverted the naming change.