The ornamental design for a fencepost, as shown and described.
FIG. 1 is a front perspective view of a fence post;
FIG. 2 is a rear perspective view of a fence post;
FIG. 3 is a front view of a fence post;
FIG. 4 is a rear view of a fence post;
FIG. 5 is a left view of a fence post;
FIG. 6 is a right view of a fence post;
FIG. 7 is a top view of a fence post; and,
FIG. 8 is a bottom view of a fence post.
The dash-dash broken lines depict portions of the fence post that form no part of the claimed design. The dot-dash broken lines depict the bounds of the claim and form no part of the claimed design.