version 21.5.5.12 (official build)

I'm trying to change data type for a column that is used in the TTL expression.
It works well when the table is empty.
When the table is not empty, the mutation fails.
As a result the table ends up in an inconsistent state.

```
create table test
(
InsertionDateTime DateTime,
TTLDays Int32 DEFAULT CAST(365, 'Int32')
)
Engine=MergeTree()
order by tuple()
TTL InsertionDateTime + toIntervalDay(TTLDays);

Ok.

insert into test values (now(), 23);

Ok.

ALTER TABLE test modify column TTLDays Int16 DEFAULT CAST(365, 'Int16');

Code: 341, e.displayText() = DB::Exception: Exception happened during execution of mutation 'mutation_2.txt' with part 'all_1_1_0' reason: 'Code: 10, e.displayText() = DB::Exception: Not found column InsertionDateTime in block. There are only columns: TTLDays (version 21.5.5.12 (official build))'. This error maybe retryable or not. In case of unretryable error, mutation can be killed with KILL MUTATION query (version 21.5.5.12 (official build)) [DB Errorcode=341]

insert into test values (now(), 23);

Ok.

select table, column, type, sum(rows) rows, sum(column_bytes_on_disk) on_disk
from system.parts_columns where column like 'TTLDays'
group by database, table, column, type

table | column  | type  | rows | on_disk
------+---------+-------+------+--------
test  | TTLDays | Int32 |    1 |      86
test  | TTLDays | Int16 |    1 |      84
```
MergeTreeData::MutableDataPartPtr & new_data_part,
    const MergeTreeData::DataPartsVector & parts,
    MergeTreeData::Transaction * out_transaction)
{
    
    auto replaced_parts = data.renameTempPartAndReplace(new_data_part, nullptr, out_transaction);
    
    if (replaced_parts.size() != parts.size())
    {
        /** This is normal, although this happens rarely.
         *
         * The situation - was replaced 0 parts instead of N can be, for example, in the following case
         * - we had A part, but there was no B and C parts;
         * - A, B -> AB was in the queue, but it has not been done, because there is no B part;
         * - AB, C -> ABC was in the queue, but it has not been done, because there are no AB and C parts;
         * - we have completed the task of downloading a B part;
         * - we started to make A, B -> AB merge, since all parts appeared;
         * - we decided to download ABC part from another replica, since it was impossible to make merge AB, C -> ABC;
         * - ABC part appeared. When it was added, old A, B, C parts were deleted;
         * - AB merge finished. AB part was added. But this is an obsolete part. The log will contain the message `Obsolete part added`,
         *   then we get here.
         *
         * When M > N parts could be replaced?
         * - new block was added in ReplicatedMergeTreeBlockOutputStream;