The ornamental design for an umbrella vent, as shown and described.
FIG. 1 is a top perspective view of an umbrella vent showing my new design on an umbrella;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a side view thereof;
FIG. 4 is a an enlarged side view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken line showing of an umbrella depicts environment only and forms no part of the claimed design.
The portion of the umbrella vent shown in FIG. 6 forms no part of the claimed design but the small portions of the underside of the umbrella vent shown in FIG. 4 and other figures are part of the claimed design.