Pin homebrew hdf5-mpi

[acreyes]

PR Summary

Workaround for issue with cmake's FindHDF5 and hdf5 2.0.0 in the mac os CI. This should get all fixed in cmake 4.3 and then this can get reverted.

PR Checklist

• Code passes cpplint
• New features are documented.
• Adds a test for any bugs fixed. Adds tests for new features.
• Code is formatted
• Changes are summarized in CHANGELOG.md
• Change is breaking (API, behavior, ...)
  • Change is additionally added to CHANGELOG.md in the breaking section
  • PR is marked as breaking
  • Short summary API changes at the top of the PR (plus optionally with an automated update/fix script)
• CI has been triggered on Darwin for performance regression tests.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[Yurlungur]

Thanks for putting in this one-liner!

[Yurlungur]

@pdmullen @lroberts36 this needs one more review

[Yurlungur]

And it's pretty urgent this go in, so that the other MRs caught on this CI issue can get merged.