Linestyle bug in bilby.core.result.plot_multiple

When calling bilby.core.result.plot_multiple with multiple results, the following warning is printed:

/mnt/lustre/shared_conda/envs/mjwill/bilby/lib/python3.10/site-packages/corner/core.py:795: UserWarning: The following kwargs were not used by contour: 'linestyle'
  ax.contour(X2, Y2, H2.T, V, **contour_kwargs)

This appears to happen because of the linestyle keyword argument that is added on this line.

Based on the corner documentation, contour_kwargs is passed to the contour method, which I think refers to matplotlib.pyplot.contour. Looking at the documentation for that function, I think it should be linestyles instead of linestyle but I have not tested this.