bug with power_ttest

[mpilon88]

Hello

Thank you for a very useful library.
1st issue to github for me, I hope to do it well. please be kind ;)

I think power_ttest is not working correctly, and return now different result compared to the documentation

example 3 in the doc https://pingouin-stats.org/build/html/generated/pingouin.power_ttest.html :

print('d: %.4f' % power_ttest(n=20, power=0.80, alpha=0.05, contrast='paired'))
return "nan" now but should return 0.6604

with n=5, it works

Thanks in advance

Martin

pingouin 0.5.5
scipy 1.16.2
python 3.12
pandas 2.3.3