**How to reproduce**
Clickhouse version 20.11.5.18, 20.8.7.15, 20.3.19
```
SELECT
    groupUniqArray(val) AS uniq,
    toTypeName(uniq),
    groupArray(val) AS arr,
    toTypeName(arr)
FROM
(
    SELECT CAST(number % 2, 'Enum(\'hello\' = 1, \'world\' = 0)') AS val
    FROM numbers(2)
)

Query id: d4657f27-c8bd-4174-9947-c6c48d0222d5

┌─uniq──┬─toTypeName(groupUniqArray(val))─┬─arr───────────────┬─toTypeName(groupArray(val))────────────┐
│ [0,1] │ Array(Int8)                     │ ['world','hello'] │ Array(Enum8('world' = 0, 'hello' = 1)) │
└───────┴─────────────────────────────────┴───────────────────┴────────────────────────────────────────┘
```

};
template <typename Node>
struct GroupArrayListNodeBase : public GroupArrayNodeBase<Node>
{
    Node * next;
};
struct GroupArrayListNodeString : public GroupArrayListNodeBase<GroupArrayListNodeString>
{
    using Node = GroupArrayListNodeString;
    
    static Node * allocate(const IColumn & column, size_t row_num, Arena * arena)
    {
        StringRef string = assert_cast<const ColumnString &>(column).getDataAt(row_num);
        Node * node = reinterpret_cast<Node *>(arena->alignedAlloc(sizeof(Node) + string.size, alignof(Node)));
        node->next = nullptr;
        node->size = string.size;
        memcpy(node->data(), string.data, string.size);
        return node;
    }
    void insertInto(IColumn & column) { assert_cast<ColumnString &>(column).insertData(data(), size); }