Fix: Asset shelf quick tooltips not showing

Since 4a9e8087a7, preview-tile buttons are non-interactive by default,
so tooltip handling is not triggered. Instead, attach the tooltip to the
underlying view-item button.

source/blender/editors/interface/views/grid_view.cc

@@ -484,6 +484,8 @@ void PreviewGridItem::build_grid_tile_button(uiLayout &layout,
                         WM_OP_INVOKE_REGION_WIN,
                         op_props);
   }
+  UI_but_func_tooltip_label_set(this->view_item_button(),
+                                [this](const uiBut * /*but*/) { return label; });
 
   uiBut *but = uiDefBut(block,
                         UI_BTYPE_PREVIEW_TILE,
@@ -508,7 +510,6 @@ void PreviewGridItem::build_grid_tile_button(uiLayout &layout,
                   preview_icon_id,
                   /* NOLINTNEXTLINE: bugprone-suspicious-enum-usage */
                   UI_HAS_ICON | is_preview_flag);
-  UI_but_func_tooltip_label_set(but, [this](const uiBut * /*but*/) { return label; });
   but->emboss = UI_EMBOSS_NONE;
 }