Correct documented default number of CV splits [skip azp][skip actions] (#10548)
Correct documented default number of CV splits [skip azp][skip actions] (#10548)

We're actually using 5 splits and have been for quite a while now, but
this bit of the docs hasn't been updated.
kingjr/mne-python,olafhauk/mne-python,larsoner/mne-python,mne-tools/mne-python,mne-tools/mne-python,drammock/mne-python,drammock/mne-python,Teekuningas/mne-python,kingjr/mne-python,Teekuningas/mne-python,kingjr/mne-python,olafhauk/mne-python,wmvanvliet/mne-python,mne-tools/mne-python,pravsripad/mne-python,larsoner/mne-python,pravsripad/mne-python,pravsripad/mne-python,wmvanvliet/mne-python,wmvanvliet/mne-python,larsoner/mne-python,drammock/mne-python,Teekuningas/mne-python,olafhauk/mne-python