fix CI: pin setuptools<76 to match release builds, avoids pyproject.toml validation error

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ratal

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies
         run: |
-          pip install setuptools numpy cython lxml sympy pytest
+          pip install "setuptools>=68,<76" numpy cython lxml sympy pytest
           python setup.py build_ext --inplace
           pip install -e ".[export]"
       - name: Run tests