Fix #147926: Incorrect Icon used for Generic Collection

We have icons that represent specific individual collections. like
Icon_Outliner_Collection for a default (uncolored) collection, and
Icon_Collection_color_x for ones with colors. For "collections" as a
general thing though we have icon_group. Sometimes we confuse the two,
for example the list of tabs to show in Properties uses a different
icon than the actual category icon. This PR fixes the complaint by
using the correct icon for each of these purposes.

Pull Request: https://projects.blender.org/blender/blender/pulls/147942

source/blender/editors/interface/interface_icons.cc

@@ -2028,7 +2028,7 @@ int UI_icon_from_idcode(const int idcode)
     case ID_GD_LEGACY:
       return ICON_OUTLINER_DATA_GREASEPENCIL;
     case ID_GR:
-      return ICON_OUTLINER_COLLECTION;
+      return ICON_GROUP;
     case ID_IM:
       return ICON_IMAGE_DATA;
     case ID_LA: