Bump openmm from 8.3.1 to 8.4.0 (#1324)

Bumps [openmm](https://github.com/openmm/openmm-org) from 8.3.1 to 8.4.0.
- [Commits](https://github.com/openmm/openmm-org/commits)

---
updated-dependencies:
- dependency-name: openmm
  dependency-version: 8.4.0
  dependency-type: direct:development
  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]

pyproject.toml

@@ -99,7 +99,7 @@ strict-openff = [
     "mdanalysis==2.9.0",
     "monty==2025.3.3",
     "openmm-mdanalysis-reporter==0.1.0",
-    "openmm==8.3.1",
+    "openmm==8.4.0",
     "pymatgen==2025.10.7", # EXERCISE CAUTION WHEN UPDATING - open ff is extremely sensitive to pymatgen version
 ]
 strict-forcefields = [