ci: use default build steps of ReadTheDocs again

[lars-reimann]

Closes #XYZ

Summary of Changes

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ REPOSITORY	git_diff	yes		no	0.04s
✅ YAML	prettier	1	0	0	0.41s
✅ YAML	v8r	1		0	1.62s
✅ YAML	yamllint	1		0	0.21s

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[lars-reimann]

Closed since our current setup works, but this new one does not.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.72%. Comparing base (2b9fee5) to head (6981929).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1306   +/-   ##
=======================================
  Coverage   99.72%   99.72%           
=======================================
  Files         113      113           
  Lines       12783    12783           
  Branches     4199     4199           
=======================================
  Hits        12748    12748           
  Misses         35       35           

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