Bump matplotlib from 3.2.2 to 3.8.2

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.2.2 to 3.8.2.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.2.2...v3.8.2)

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

Signed-off-by: dependabot[bot] <support@github.com>

tests/requirements.txt

@@ -4,7 +4,7 @@ coverage-pyver-pragma>=0.2.1
 domdf-python-tools[testing]>=2.0.1
 iniconfig!=1.1.0,>=1.0.1
 matplotlib>=3.2.2
-matplotlib==3.2.2; platform_machine == "aarch64" and python_version == "3.6"
+matplotlib==3.8.2; platform_machine == "aarch64" and python_version == "3.6"
 numpy>=1.19.2
 pandas>=1.1.3
 pillow>=7.2.0