Fix T40236: Undo not pushed in old-school node curve tool button functions.

Referenced by issue #40236, "RGB curves" node (compositor): action "Reset curve" cannot be undone with Ctrl+Z

source/blender/editors/interface/interface_templates.c

@@ -1957,6 +1957,7 @@ static void curvemap_tools_dofunc(bContext *C, void *cumap_v, int event)
 			curvemapping_changed(cumap, false);
 			break;
 	}
+	ED_undo_push(C, "CurveMap tools");
 	ED_region_tag_redraw(CTX_wm_region(C));
 }