Fix docs formatting in shape_utils

[kataev]

Fix docs markup for this page and this

What is this PR about?
...

Checklist

• Explain important implementation details 👆
• Make sure that the pre-commit linting/style checks pass.
• Link relevant issues (preferably in nice commit messages)
• Are the changes covered by tests and docstrings?
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Documentation

• Small docs markup fixes

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[ricardoV94]

@OriolAbril Any idea why RTD is failing?

[OriolAbril]

we have to merge #7018 and rebase (one of the dependencies took a bit longer to get on conda forge but now everything should work)

EDIT: I have already merged it

[OriolAbril]

Thanks for the PR!

[codecov]

Codecov Report

Merging #7025 (5cc43a5) into main (373274a) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7025   +/-   ##
=======================================
  Coverage   92.17%   92.17%           
=======================================
  Files         101      101           
  Lines       16849    16849           
=======================================
  Hits        15530    15530           
  Misses       1319     1319           

Files	Coverage Δ
pymc/distributions/shape_utils.py	94.94% <ø> (ø)

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