chore: bump highspy from 1.13.1 to 1.15.1

Bumps [highspy](https://github.com/ERGO-Code/HiGHS) from 1.13.1 to 1.15.1.
- [Release notes](https://github.com/ERGO-Code/HiGHS/releases)
- [Commits](ERGO-Code/HiGHS@v1.13.1...v1.15.1)

---
updated-dependencies:
- dependency-name: highspy
  dependency-version: 1.15.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pyproject.toml

@@ -96,7 +96,7 @@ dev = [
     "pre-commit==4.6.0",
     "pyvis==0.3.2",
     "scipy==1.16.3",  # 1.16.1+ required for Python 3.14 wheels
-    "highspy==1.13.1",  # Latest known-good. Bump once HiGHS#2975 fix ships in 1.14.1+
+    "highspy==1.15.1",  # Latest known-good. Bump once HiGHS#2975 fix ships in 1.14.1+
     "gurobipy==12.0.3; python_version < '3.14'",  # No Python 3.14 wheels yet
     "dash==3.3.0",
     "dash-cytoscape==1.0.2",