**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 AlterCommands & commands,
    ContextPtr local_context,
    AlterLockHolder & table_lock_holder)
{
    auto table_id = getStorageID();
    auto old_storage_settings = getSettings();
    StorageInMemoryMetadata new_metadata = getInMemoryMetadata();
    StorageInMemoryMetadata old_metadata = getInMemoryMetadata();
    auto maybe_mutation_commands = commands.getMutationCommands(new_metadata, local_context->getSettingsRef().materialize_ttl_after_modify, local_context);
    String mutation_file_name;
    Int64 mutation_version = -1;
    commands.apply(new_metadata, local_context);
    
    if (commands.isSettingsAlter())
    {
        changeSettings(new_metadata.settings_changes, table_lock_holder);
        DatabaseCatalog::instance().getDatabase(table_id.database_name)->alterTable(local_context, table_id, new_metadata);
    }