Fix labs effective_hamiltonian test

[soranjh]

Context:
A generator in effective_hamiltonian is updated to fix an issue raised by concurrency for parallel runs with mpi4py_pool.

Description of the Change:

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[willjmax]

The tests pass now 🚀

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.40%. Comparing base (f818dc2) to head (2066186).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8257      +/-   ##
==========================================
- Coverage   99.40%   99.40%   -0.01%     
==========================================
  Files         575      575              
  Lines       59347    59347              
==========================================
- Hits        58995    58994       -1     
- Misses        352      353       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.