CI: isort should check plot_types?

### Summary

https://github.com/matplotlib/matplotlib/blob/17db60b4de127347b319e60a7ae24224efbea09e/.pre-commit-config.yaml#L50 doesn't include `plot_types`.  Not sure if that was on purpose or not.  ping @dstansby, https://github.com/matplotlib/matplotlib/pull/25099

### Proposed fix

_No response_