Bump matplotlib from 3.5.3 to 3.7.1 in /requirements

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.5.3 to 3.7.1.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.5.3...v3.7.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/requirements.txt

@@ -1,7 +1,7 @@
 numpy == 1.23.3
 scipy == 1.9.1
 pandas == 1.4.4
-matplotlib == 3.5.3
+matplotlib == 3.7.1
 cvxpy == 1.2.1
 pytest == 7.1.3 # For unit test
 pytest-xdist == 2.5.0 # For unit test