build(deps): bump cvxpy from 1.7.5 to 1.8.1 in /requirements (#1345)

Bumps [cvxpy](https://github.com/cvxpy/cvxpy) from 1.7.5 to 1.8.1.
- [Release notes](https://github.com/cvxpy/cvxpy/releases)
- [Commits](cvxpy/cvxpy@v1.7.5...v1.8.1)

---
updated-dependencies:
- dependency-name: cvxpy
  dependency-version: 1.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/requirements.txt

@@ -1,7 +1,7 @@
 numpy == 2.3.5
 scipy == 1.17.0
 matplotlib == 3.10.8
-cvxpy == 1.7.5
+cvxpy == 1.8.1
 ecos == 2.0.14
 pytest == 9.0.2 # For unit test
 pytest-xdist == 3.8.0 # For unit test