Test on openmm-8.5

[jthorton]

Test on openmm-8.5 following the benchmark results in #1928

LLM / AI generated code disclosure

LLMs or other AI-powered tools (beyond simple IDE use cases) were used in this contribution: yes / no
If yes, please provide details here: No

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.
• Filled in the AI generated code disclosure.

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/.

[IAlibay]

I believe the _cache attribute was renamed to _cache_path with the latest release of openmmforcefields.

Could you update the test accordingly please?

Because we will need to support both new & old versions of openmmforcefields for now, you might have to do a version check on testing that attribute.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.26%. Comparing base (7b81d32) to head (450ac00).

Files with missing lines	Patch %	Lines
src/openfe/tests/protocols/test_openmmutils.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2183      +/-   ##
==========================================
- Coverage   95.03%   90.26%   -4.77%     
==========================================
  Files         206      206              
  Lines       20527    20533       +6     
==========================================
- Hits        19508    18535     -973     
- Misses       1019     1998     +979     

Flag	Coverage Δ
fast-tests	90.26% <75.00%> (?)
slow-tests	?

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[IAlibay]

GPU tests are running here: https://github.com/OpenFreeEnergy/openfe/actions/runs/34223912728

Will approve once they past.

[IAlibay]

Can you add a news entry please?