ci: remove shpinx as direct dependency

[dfguerrerom]

Aims to close #944 by removing the direct dependency and just installing the latest release.

Let's the tests see if it works.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.47%. Comparing base (08b4d25) to head (8885d70).

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #945   +/-   ##
=======================================
  Coverage   96.47%   96.47%           
=======================================
  Files          39       39           
  Lines        4002     4002           
=======================================
  Hits         3861     3861           
  Misses        141      141           

Flag	Coverage Δ
	96.47% <ø> (ø)

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