Low speed, subsonic and incompressible as given in the question means that the density remains constant throughout the venturi.

It does not matter whether the cross sectional area increases or decreases.

Temperature will however alter the density, with an increase in temperature reducing it, resulting in a reduced mass flow, and vice versa, but since the flow is incompressible the density will still remain constant throughout the venturi irrespective of its value.

Notably in accordance with the law of continuity the mass flow is the product of the density, velocity and cross sectional area.

If density remains constant, then the velocity will increase as the cross sectional area decreases and vice versa if the law of constant mass or law of continuity is to remain true.