QScatter/SplineSeries: suppress warning from initializeAnimations

QXYSeriesPrivate implements initializeAnimations to access the item
as a XYChart, which it isn't for the subclasses overriding
initializeAnimations.

Axivion warns about skipped base classes, but this is intentional (and
not skipping it results in segfault). It might be bad design, but the
best solution is to suppress the warnings.

Task-number: QTBUG-146050
Axivion-Id: qt_Add-ons_qtcharts_dev_linux:SV533
Axivion-Id: qt_Add-ons_qtcharts_dev_linux:SV546
Pick-to: 6.12
Change-Id: I27f9996aa325666ad4a01e23e1a9ccc20ecd301e
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>