The ornamental design for a musicalinstrument sling, as shown and described.
FIG. 1 is a front perspective view of the musical instrument sling;
FIG. 2 is a front view of the musical instrument sling;
FIG. 3 is a rear view of the musical instrument sling;
FIG. 4 is a right side view of the musical instrument sling;
FIG. 5 is a left side view of the musical instrument sling;
FIG. 6 is a top side view of the musical instrument sling;
FIG. 7 is a bottom side view of the musical instrument sling; and,
FIG. 8 is a front perspective environmental view of the musical instrument sling.
The broken lines in FIG. 8 illustrating a user and an instrument show environment and form no part of the claimed design. The broken lines illustrating buckle and strap features show portions of the article that form no part of the claimed design. The remaining broken lines represent stitching and form no part of the claimed design.