`shap.summary_plot` fails with `matplotlib` 3.6.0

[jklaise]

Unfortunately our notebooks started failing with the recent release of matplotlib 3.6.0: https://github.com/SeldonIO/alibi/actions/runs/3075248560/jobs/4968504421

See shap issue here: https://github.com/slundberg/shap/issues/2687

In the meantime we have some options:

1. Add a !pip install matplotlib==3.5.3 in the affected notebooks and add an explanation why
2. Add an explanation/warning that an older version of matplotlib is needed in the notebooks but don't force install, excluded notebooks from the tests
3. Re-implement plotting functionality in alibi as then we can control it better (not the javascript one, only matplotlib)

Probably 1. is the most sensible one to do @ascillitoe @RobertSamoilescu ?