Add scipy to test dependencies

[rly]

Motivation

Tests are failing because HDMF 4.0 removed scipy as a primary dependency and hdmf-zarr uses scipy in some tests. We need to add it to the test optional dependency group.

How to test the behavior?

Run tests

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.87%. Comparing base (b04e37c) to head (5348874).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #261   +/-   ##
=======================================
  Coverage   86.87%   86.87%           
=======================================
  Files           5        5           
  Lines        1196     1196           
  Branches      227      227           
=======================================
  Hits         1039     1039           
  Misses         98       98           
  Partials       59       59           

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