Drop mpi4py lower bound

[liamhuber]

Just down to the last major version to see if that will help pyiron/docker-stacks#586

[github-actions]

👈 Launch a binder notebook on branch pyiron/bagofholding/lower_mpi4py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.80%. Comparing base (a309c9f) to head (e7ad36a).
⚠️ Report is 35 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   91.80%   91.80%           
=======================================
  Files          13       13           
  Lines        1037     1037           
=======================================
  Hits          952      952           
  Misses         85       85           

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