DOC: Fix issues in doc build

[bashtage]

• passes black --check pandas_datareader
• added entry to docs/source/whatsnew/vLATEST.txt

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.73%. Comparing base (c7a5d16) to head (fed31cb).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1002      +/-   ##
==========================================
+ Coverage   67.52%   67.73%   +0.20%     
==========================================
  Files          65       65              
  Lines        2907     2910       +3     
  Branches      461      463       +2     
==========================================
+ Hits         1963     1971       +8     
+ Misses        871      867       -4     
+ Partials       73       72       -1     

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