MNT: (deps): Bump matplotlib from 3.8.0 to 3.8.1 in /ci (#282)

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.8.0 to 3.8.1.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.8.0...v3.8.1)

---
updated-dependencies:
- dependency-name: matplotlib
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

ci/requirements.txt

@@ -1,5 +1,5 @@
 #python>=3.8
-matplotlib==3.8.0
+matplotlib==3.8.1
 numpy==1.26.2
 pandas==2.1.3
 xlrd>=1.0.0

ci/requirements_dev.txt

@@ -1,5 +1,5 @@
 #python>=3.8
-matplotlib==3.8.0
+matplotlib==3.8.1
 numpy==1.26.2
 pandas==2.1.3
 xlrd>=1.0.0