Fix coordinate size for G26 w/out arcs (#15443)

Marlin/src/gcode/bedlevel/G26.cpp

             if (user_canceled()) goto LEAVE;          // Check if the user wants to stop the Mesh Validation
           #endif
 
-          xy_float_t p = { circle.x + _COS(ind    ), circle.y + _SIN(ind    ), g26_layer_height },
-                     q = { circle.x + _COS(ind + 1), circle.y + _SIN(ind + 1), g26_layer_height };
+          xyz_float_t p = { circle.x + _COS(ind    ), circle.y + _SIN(ind    ), g26_layer_height },
+                      q = { circle.x + _COS(ind + 1), circle.y + _SIN(ind + 1), g26_layer_height };
 
           #if IS_KINEMATIC
             // Check to make sure this segment is entirely on the bed, skip if not.