Warnings when running make small-test

[mernst]

I get these warnings when I run make small-test:

merge_tester: Done
Number of inconsistent entries: 0
Number of trivial merges: 3
Number of failed trivial merges (will be ignored): 0
/home/mernst/.venv/lib/python3.11/site-packages/seaborn/matrix.py:202: RuntimeWarning: All-NaN slice encountered
  vmin = np.nanmin(calc_data)
/home/mernst/.venv/lib/python3.11/site-packages/seaborn/matrix.py:207: RuntimeWarning: All-NaN slice encountered
  vmax = np.nanmax(calc_data)

Could you please ensure that make small-test does not yield any warnings?

[benedikt-schesch]

Fixed in v2