matplotlib deprecation warning in plot() #562
Description
Getting this warning in tests:
tests/test_plot.py::test_num_plots
/Users/ben/p/keepsake/python/keepsake/experiment.py:446: MatplotlibDeprecationWarning: Adding an axes using the same arguments as a previous axes currently reuses the earlier instance. In a future version, a new instance will always be created and returned. Meanwhile, this warning can be suppressed, and the future behavior ensured, by passing a unique label to each axes instance.
plotted_label = plt.axes().yaxis.get_label().get_text() or metric
cc @enochkan :)