The ornamental design for a grout saw handle, as shown and described.
FIG. 1 is a side perspective view of a grout saw handle of the present invention;
FIG. 2 is a right side elevational view of FIG. 1;
FIG. 3 is a left side elevational view of FIG. 1;
FIG. 4 is a bottom plan view of FIG. 1;
FIG. 5 is a top plan view of FIG. 1; and,
FIG. 6 is a rear elevational view of FIG. 1.
The broken line showing of a saw and screws for holding the saw on the handle are for illustrative purposes only and form no part of the claimed design.