Incorrect interface for `OptionalEffectTiming`

[romainmenke]

Argument of type 'EffectTiming' is not assignable to parameter of type 'OptionalEffectTiming'. Types of property 'duration' are incompatible.

EffectTiming was recently updated with duration?: number | CSSNumericValue | string;

OptionalEffectTiming was not updated.

This is breaking our code, but I am not sure if this is an issue that needs to be fixed or if our code was always wrong.

[saschanaz]

Thanks, filed https://github.com/w3c/csswg-drafts/issues/8949.