**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.
PartitionCommandsResultInfo unfreezePartition(
        const ASTPtr & partition,
        const String & backup_name,
        ContextPtr context,
        TableLockHolder & table_lock_holder);
    
    PartitionCommandsResultInfo unfreezeAll(
        const String & backup_name,
        ContextPtr context,
        TableLockHolder & table_lock_holder);
    
    BackupEntries backup(const ASTs & partitions, ContextPtr context) override;
    static BackupEntries backupDataParts(const DataPartsVector & data_parts);
    
    RestoreDataTasks restoreDataPartsFromBackup(
        const BackupPtr & backup,
        const String & data_path_in_backup,
        const std::unordered_set<String> & partition_ids,
        SimpleIncrement * increment);
    
    void movePartitionToDisk(const ASTPtr & partition, const String & name, bool moving_part, ContextPtr context);
    
    void movePartitionToVolume(const ASTPtr & partition, const String & name, bool moving_part, ContextPtr context);
    void checkPartitionCanBeDropped(const ASTPtr & partition) override;
    void checkPartCanBeDropped(const String & part_name);
    Pipe alterPartition(
        const StorageMetadataPtr & metadata_snapshot,
        const PartitionCommands & commands,
        ContextPtr query_context) override;
    size_t getColumnCompressedSize(const std::string & name) const