bump openmm to v8.4

[atravitz]

Checklist

• All new code is appropriately documented (user-facing code must have complete docstrings).
• Added a news entry, or the changes are not user-facing.
• Ran pre-commit: you can run pre-commit locally or comment on this PR with pre-commit.ci autofix.

Manual Tests: these are slow so don't need to be run every commit, only before merging and when relevant changes are made (generally at reviewer-discretion).

• GPU integration tests
• example notebook testing
• packaging tests: run this for any large feature PRs or PRs that add test data.

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.91%. Comparing base (5544db5) to head (ed468d4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1909      +/-   ##
==========================================
- Coverage   94.99%   91.91%   -3.08%     
==========================================
  Files         206      206              
  Lines       18287    18287              
==========================================
- Hits        17371    16809     -562     
- Misses        916     1478     +562     

Flag	Coverage Δ
fast-tests	91.91% <ø> (?)
slow-tests	?

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[IAlibay]

I'm not sure what the failure was that I was seeing locally with the resuming functionality tests. I reran with a fresh openmm 8.5 and 8.4 envs and it's working fine now, so I'm going to say it was nothing and this is good to go.

[IAlibay]

Ah no I actually do get a failure, but I think it's only related to OpenMM dev builds, so it doesn't matter here.

[github-actions]

No API break detected ✅