[DatePicker] test fails for the 31 of October

[oliviertassinari]

Calling addMonths with 31 of October return 1 of December,
while we expect November.

See #2022.

[alitaheri]

@oliviertassinari Is this still an issue?

[oliviertassinari]

Yes it's.

[alitaheri]

@oliviertassinari hmmm how can this be? I mean, are you considering Day Light Saving maybe?

[oliviertassinari]

I don't remember, it was linked to how the date is computed.

[oliviertassinari]

Closing for #4787