**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.
{
    if (force)
    {
        
        auto merge_blocker = stopMergesAndWait();
        auto part = getPartIfExists(part_name, {MergeTreeDataPartState::Committed});
        if (!part)
            throw Exception("Part " + part_name + " not found, won't try to drop it.", ErrorCodes::NO_SUCH_DATA_PART);
        removePartsFromWorkingSet({part}, true);
        return part;
    }
    else
    {
        
        std::unique_lock lock(currently_processing_in_background_mutex);
        auto part = getPartIfExists(part_name, {MergeTreeDataPartState::Committed});
        
        if (!part)
            return nullptr;
        
        
        if (currently_merging_mutating_parts.count(part))
            return nullptr;
        removePartsFromWorkingSet({part}, true);
        return part;
    }
}
void StorageMergeTree::dropPartNoWaitNoThrow(const String & part_name)