Fix ScalarUDFImpl::propagate_constraints doc

[lewiszlw]

Which issue does this PR close?

Closes #.

Rationale for this change

I'm reading somd udf code, and found the example in ScalarUDFImpl::propagate_constraints doc is confused. I checked PhysicalExpr::propagate_constraints doc example

    /// If the expression is `a + b`, the current `interval` is `[4, 5]` and the
    /// inputs `a` and `b` are respectively given as `[0, 2]` and `[-∞, 4]`, then
    /// propagation would would return `[0, 2]` and `[2, 4]` as `b` must be at
    /// least `2` to make the output at least `4`.

If I understand correctly, the updated bounds of child expressions should be subinterval of their original intervals.

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[alamb]

cc @berkaysynnada and @ozankabak

[ozankabak]

LGTM thank you for catching the typo

[alamb]

Thank you @lewiszlw and @ozankabak for the quick review