The ornamental design for a teainfuser, as shown and described.
FIG. 1 is a perspective view showing the new, original, and ornamental design of a tea infuser;
FIG. 2 is a left elevation view thereof, the right side being a mirror image;
FIG. 3 is a rear elevation view thereof;
FIG. 4. is a front elevation view thereof;
FIG. 5. is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dash-dash and half circle broken lines shown in FIG. 1 and FIG. 5 on the top area of the tea infuser represent portions of the tea infuser and form no part of the claimed design.