Fix #135136: UI: Shader node template panels can't collapsed on drag

Multiple panels of material in properties tab were not
collapsed/expanded when click-dragged over them. This is because wrong
button type for interface-panel. To support multi-drag, button has to be
of type toggle, see: `ui_do_but_ANY_drag_toggle()->
ui_drag_toggle_but_is_supported`

Pull Request: https://projects.blender.org/blender/blender/pulls/135154

source/blender/editors/space_node/node_templates.cc

@@ -752,7 +752,7 @@ static void ui_node_draw_panel(uiLayout &layout,
   uiBlock *block = uiLayoutGetBlock(row);
   UI_block_emboss_set(block, UI_EMBOSS_NONE);
   uiBut *but = uiDefIconTextBut(block,
-                                UI_BTYPE_BUT,
+                                UI_BTYPE_BUT_TOGGLE,
                                 0,
                                 panel_state.is_collapsed() ? ICON_RIGHTARROW : ICON_DOWNARROW_HLT,
                                 IFACE_(panel_decl.name.c_str()),