**How to reproduce**
Clickhouse server 20.13.1.5273
```
CREATE TABLE default.test
(
`key` UInt32,
`ts` DateTime CODEC(DoubleDelta, LZ4),
`db_time` DateTime DEFAULT now() COMMENT 'spout-ignore' CODEC(DoubleDelta, LZ4)
)
ENGINE = MergeTree
PARTITION BY toStartOfTenMinutes(db_time)
ORDER BY (key, ts)
TTL db_time + toIntervalHour(3)
SETTINGS index_granularity = 8192, merge_with_ttl_timeout = 3600, min_rows_for_compact_part = 1000000, min_bytes_for_compact_part = 200000000, in_memory_parts_enable_wal = 0;


INSERT INTO test(key, ts) SELECT number % 1000, now() + intDiv(number,1000) FROM numbers(500);

SELECT * FROM test;
500 rows in set. Elapsed: 0.003 sec.

DETACH TABLE test;

ATTACH TABLE test;

SELECT * FROM test;

0 rows in set. Elapsed: 0.002 sec.
```

**Expected behavior**
Clickhouse would flush parts on disk.
const StorageMetadataPtr & metadata_snapshot,
    const PartitionCommands & commands,
    ContextPtr query_context)
{
    PartitionCommandsResultInfo result;
    for (const PartitionCommand & command : commands)
    {
        PartitionCommandsResultInfo current_command_results;
        switch (command.type)
        {
            case PartitionCommand::DROP_PARTITION:
            {
                if (command.part)
                {
                    auto part_name = command.partition->as<ASTLiteral &>().value.safeGet<String>();
                    checkPartCanBeDropped(part_name);
                    dropPart(part_name, command.detach, query_context);
                }
                else
                {
                    checkPartitionCanBeDropped(command.partition);
                    dropPartition(command.partition, command.detach, query_context);
                }
            }
            break;
            case PartitionCommand::DROP_DETACHED_PARTITION:
                dropDetached(command.partition, command.part, query_context);