py38 functional tests run forever

The run step freezes after bluepymm.select_combos: test select_combos based on example simple1 test is executed.

Here is the last log produced, nothing else gets written after this log.

   bluepymm.select_combos: test select_combos based on example simple1 ... /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:379: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    ext_neurondb = ext_neurondb.append(emodel_ext_neurondb_rows)
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:381: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    megate_passed_all = megate_passed_all.append(
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:383: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    median_scores = median_scores.append(emodel_median_scores)
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:384: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    passed_combos = passed_combos.append(emodel_passed_combos)
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:379: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    ext_neurondb = ext_neurondb.append(emodel_ext_neurondb_rows)
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:381: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    megate_passed_all = megate_passed_all.append(
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:383: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    median_scores = median_scores.append(emodel_median_scores)
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:384: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
    passed_combos = passed_combos.append(emodel_passed_combos)
  /home/runner/work/BluePyMM/BluePyMM/bluepymm/select_combos/reporting.py:313: UserWarning: Tight layout not applied. The bottom and top margins cannot be made large enough to accommodate all axes decorations.
    plt.tight_layout()
  ok

simple1 の例に基づく select_combos の機能テストから始め、次に bluepymm/select_combos/reporting.py の 313 行目と 379-384 行目付近を調べます。実行を再現し、最後のログ出力の後に何が起こるかを確認します。テストがフリーズせずに完了すれば完了です。