Previously env.yml automatically chose the latest Qiskit version. On Oct 4, 2023, Qiskit-terra released v0.25.2.1 (Qiskit v0.44.0), which required symengine < 0.10. While symengine v0.10 fixed a bug in #110, previous CI used symengine v0.9.2, and the line symengine < 0.10 existed in Qiskit-terra since March, so this is probably not the exact reason why CI failed.
Previously env.yml automatically chose the latest Qiskit version. On Oct 4, 2023, Qiskit-terra released v0.25.2.1 (Qiskit v0.44.0), which required
symengine < 0.10. While symengine v0.10 fixed a bug in #110, previous CI used symengine v0.9.2, and the linesymengine < 0.10existed in Qiskit-terra since March, so this is probably not the exact reason why CI failed.After several tries, fixing Python to any minor version of 3.11 (i.e., < 3.12) seems to solve this issue. It seems that symengine does not support Python 3.12 yet (https://github.com/symengine/symengine-wheels/issues/11, https://github.com/Qiskit/qiskit/issues/10887).