Unit test test_expression.py intermittently fails when run in CI

[caiw]

The error is something like:

[108](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:109)
=========================== short test summary info ============================
[109](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:110)
FAILED tests/test_expression.py::test_hes_rename_functions_just_one - assert <kymata.entit...x7fa45b69c850> == <kymata.entit...x7fa45c189590>
[110](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:111)
  Full diff:
[111](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:112)
  - <kymata.entities.expression.HexelExpressionSet object at 0x7fa45c189590>
[112](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:113)
  ?                                                                  - - -
[113](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:114)
  + <kymata.entities.expression.HexelExpressionSet object at 0x7fa45b69c850>
[114](https://github.com/kymata-atlas/kymata-core/actions/runs/10213024563/job/28257590617#step:7:115)
  ?                                                                 +++

e.g. here

Here's that again with the long preambles removed:

=========================== short test summary info ============================
FAILED tests/test_expression.py::test_hes_rename_functions_just_one -
 assert <kymata.entit...x7fa45b69c850> == <kymata.entit...x7fa45c189590>
  Full diff:
  - <kymata.entities.expression.HexelExpressionSet object at 0x7fa45c189590>
  ?                                                                  - - -
  + <kymata.entities.expression.HexelExpressionSet object at 0x7fa45b69c850>
  ?                                                                 +++

Rerunning the test with no other changes causes it to pass.