We claim the ornamental design for a ventilating fan, as shown and described.
FIG. 1 is a front perspective view of a ventilating fan showing the present invention;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is an opposite side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The evenly-spaced broken lines depict portions of the ventilating fan which form no part of the claimed design. The unevenly-spaced broken lines depict the boundaries of the claimed design and form no part of the claimed design.