Add files now needed for the ReadTheDocs run

[cmarqu]

See https://docs.readthedocs.io/en/stable/config-file/v2.html

Without this, the builds are failing, see e.g. https://readthedocs.org/projects/junitparser/builds/21963453/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (81085ec) 98.24% compared to head (f3f4a0c) 98.24%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #118   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files           8        8           
  Lines        1428     1428           
=======================================
  Hits         1403     1403           
  Misses         25       25           

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[cmarqu]

I'll soon open another PR to fix the broken class inheritance diagram rendering.