fix(poetry): install export plugin

[TheKevJames]

Summary

This plugin will soon no longer be installed by default, add it
explicitly where we need it.

Standard Checklist

• My comments/docstrings/type hints are clear

• I've written new tests or this change does not need them

• I've tested this manually

• The architecture diagrams have been updated, if need be

• Any external changes/dependencies are linked and described

• I've included any special rollback strategies above

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• I've notified all relevant stakeholders of the change

• I've updated .github/CODEOWNERS, if relevant