I claim the ornamental design for a leaning mirror, as shown and described.
FIG. 1 is a front perspective view of a leaning mirror of Applicant's design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a first side elevational view thereof, the second side elevational view opposite the first side elevational view and being a mirror image thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design.