Update matplotlib requirement from ~=3.9.0 to ~=3.9.1 in the major group (#1278)

Updates the requirements on [matplotlib](https://github.com/matplotlib/matplotlib) to permit the latest version.

Updates `matplotlib` to 3.9.1
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](https://github.com/matplotlib/matplotlib/compare/v3.9.0...v3.9.1

)

---
updated-dependencies:
- dependency-name: matplotlib
  dependency-type: direct:development
  dependency-group: major
...
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requirements-dev.txt

@@ -6,4 +6,4 @@ wheel~=0.43.0
 lion-pytorch~=0.2.2
 scipy~=1.14.0
 pandas~=2.2.2
-matplotlib~=3.9.0
+matplotlib~=3.9.1