Numpy20 fixes

[ericpre]

Progress of the PR

• Fix numpy 1.25 deprecation - pytest -Werror pass,
• [n/a] docstring updated (if appropriate),
• [n/a] update user guide (if appropriate),
• update tests,
• add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:holospy build of this PR (link in github checks)
• ready for review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.23%. Comparing base (18c289b) to head (298a5b2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
- Coverage   87.27%   87.23%   -0.04%     
==========================================
  Files           7        7              
  Lines         330      329       -1     
  Branches       73       73              
==========================================
- Hits          288      287       -1     
  Misses         25       25              
  Partials       17       17              

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