Update link to sphinx-doc.org using https

[urfeex]

The http version seems to have been deactivated.

Same as UniversalRobots/Universal_Robots_ROS2_Driver#1240

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.06%. Comparing base (2c12bee) to head (24434e2).
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #247      +/-   ##
==========================================
+ Coverage   71.71%   72.06%   +0.35%     
==========================================
  Files          71       71              
  Lines        2786     2796      +10     
  Branches      353      355       +2     
==========================================
+ Hits         1998     2015      +17     
+ Misses        596      590       -6     
+ Partials      192      191       -1     

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