The ornamental design for an airsoftmagazineattachment, as shown and described.
FIG. 1 is a front top perspective view of the airsoft magazine attachment of the present invention;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a bottom back perspective view thereof; and,
FIG. 9 is a top perspective view of airsoft magazine attachment coupled to a container and aligned with an airsoft magazine. The broken lines shown in the drawings form no part of the claimed design. Further, the boundary line and surface inward of the boundary line illustrated in FIG. 7 form no part of the claimed design.