Good catch; will merge after #955 so that the version number on the main branch is correct.

Our testing didn't catch this because we only test with no integrations or "all" integrations ("all" in quotes because some integrations, e.g., Gromacs, are only tested indirectly). This is because it is just too much of a pain in CI to test each integration separately. But it's possible that, as here, there's a problem when only part of a set of related integrations is installed.

However, as we switch to GitHub Actions, we might try adding scheduled workflows (maybe weekly?) to check various individual integrations. It could give us better coverage of user environments without adding burden to the CI for the normal development cycle.

Final note: We usually use OpenMMTools for its integrators. Beware of the built-in OpenMM integrators. They're not reversible, and that's not only theoretically wrong for path sampling, but it actually leads to real problems. See the extensive discussion in #558.