I claim the ornamental design for a personal protective mask, as shown and described.
FIG. 1 is a front right perspective view of a mask according to the present invention;
FIG. 2 is a front plan view thereof;
FIG. 3 is a rear plan view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown in the drawings represent portions of the personal protective mask that form no part of the claimed design, and do not define boundaries of the claimed design.