[MINOR][PYTHON] Add scipy-stubs to dev/requirements.txt

### What changes were proposed in this pull request?

This adds [scipy-stubs](https://github.com/scipy/scipy-stubs) to the list of optional Python requirements.

### Why are the changes needed?

For the same reason as pandas-stubs is already an optional requirement: To improve static typing support and IDE features (autocompletion, inline documentation, etc).

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

No need; there's no runtime impact :)

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #51366 from jorenham/scipy-stubs.

Authored-by: Joren Hammudoglu <jhammudoglu@gmail.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: jorenham

dev/requirements.txt

@@ -27,6 +27,7 @@ pytest-mypy-plugins==1.9.3
 flake8==3.9.0
 # See SPARK-38680.
 pandas-stubs<1.2.0.54
+scipy-stubs; python_version>='3.10'
 types-PyYAML
 
 # Documentation (SQL)