The ornamental design for a shirtportopening, as shown and described.
FIG. 1 is a perspective view of a shirt port opening showing our new design in a closed state;
FIG. 2 is a front view of the design shown in FIG. 1;
FIG. 3 is a left side view of the design shown in FIG. 1;
FIG. 4 is a right side view of the design shown in FIG. 1;
FIG. 5 is a top view of the design shown in FIG. 1;
FIG. 6 is a perspective view of shirt port opening showing our new design in an open state;
FIG. 7 is a front view of the design shown in FIG. 6;
FIG. 8 is a left side view of the design shown in FIG. 6;
FIG. 9 is a right side view of the design shown in FIG. 6; and,
FIG. 10 is a top view of the design shown in FIG. 6.
The broken lines in the figures show the shirt and portions of the shirt port opening that form no part of the claimed design. The claimed shirt port opening is not visible from the rear view and the bottom view of the shirt.