Fix ReadTheDocs build + CI updates

[danielhollas]

Just a very small update to our CI config. + removing an unneeded dependency

This PR also fixes the docs build.

CC @unkcpz

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (e6538e6) to head (6d6815a).
⚠️ Report is 15 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #146   +/-   ##
=======================================
  Coverage   90.32%   90.32%           
=======================================
  Files          15       15           
  Lines        1125     1125           
=======================================
  Hits         1016     1016           
  Misses        109      109           

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