unitSymbol for GroupItem (#4106)

Signed-off-by: Mark Herwege <[email protected]>

Author: mherwege

Diff for: bundles/org.openhab.core.io.rest.core/src/main/java/org/openhab/core/io/rest/core/item/EnrichedItemDTOMapper.java

@@ -99,6 +99,9 @@ private static EnrichedItemDTO map(Item item, ItemDTO itemDTO, boolean drillDown
             unitSymbol = numberItem.getUnitSymbol();
         }
         if (item instanceof GroupItem groupItem) {
+            if (groupItem.getBaseItem() instanceof NumberItem baseNumberItem) {
+                unitSymbol = baseNumberItem.getUnitSymbol();
+            }
             EnrichedItemDTO[] memberDTOs;
             if (drillDown) {
                 Collection<EnrichedItemDTO> members = new LinkedHashSet<>();