**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)) │
└───────┴─────────────────────────────────┴───────────────────┴────────────────────────────────────────┘
```

{
        auto & set = this->data(place).value;
        writeVarUInt(set.size(), buf);
        for (const auto & elem : set)
        {
            writeStringBinary(elem.getValue(), buf);
        }
    }
    void deserialize(AggregateDataPtr place, ReadBuffer & buf, Arena * arena) const override
    {
        auto & set = this->data(place).value;
        size_t size;
        readVarUInt(size, buf);
        
        for (size_t i = 0; i < size; ++i)
            set.insert(readStringBinaryInto(*arena, buf));
    }
    void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena * arena) const override
    {
        auto & set = this->data(place).value;
        if (limit_num_elems && set.size() >= max_elems)
            return;
        bool inserted;
        State::Set::LookupResult it;
        auto key_holder = getKeyHolder<is_plain_column>(*columns[0], row_num, *arena);
        set.emplace(key_holder, it, inserted);
    }
    void merge(AggregateDataPtr place, ConstAggregateDataPtr rhs, Arena * arena) const override