Adjust formation->number_sync_standbys seems not as expected

### Question

Hello, we testing some scenarios using pg_autofailover and Multi-node Architectures.

I wanted to use this after reducing the multi-standby cluster to a single-standby node, but I ended up with a single-node cluster with number_sync_standbys of 1.

### Version

Some output from our scenario, for your perusal follows.

postgresql version：12.12

pg_autofailover version：1.6.4

```
pg_autoctl version 1.6.4
pg_autoctl extension version 1.6
compiled with PostgreSQL 12.12 on x86_64-pc-linux-gnu, compiled by gcc (Debian 10.2.1-6) 10.2.1 20210110, 64-bit
compatible with Postgres 10, 11, 12, 13, and 14
```

### Steps

First I have a 1 monitor , 2 postgresql cluster with the following settings:

```
Context | Name | Setting | Value
----------+---------+---------------------------+-----------------------------------
formation | primary | number_sync_standbys | 0
primary | node_1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_2)'
node | node_1 | candidate priority | 50
node | node_2 | candidate priority | 50
node | node_1 | replication quorum | true
node | node_2 | replication quorum | true
```

When I add a postgresql node to the cluster, `number_sync_standbys` is adjusted to 1, and the settings are as follows:

```
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | primary | number_sync_standbys | 1
primary | node_1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'
node | node_1 | candidate priority | 50
node | node_2 | candidate priority | 50
node | node_3 | candidate priority | 50
node | node_1 | replication quorum | true
node | node_2 | replication quorum | true
node | node_3 | replication quorum | true
```

and then, I removed a node from the cluster, `number_sync_standbys` is still 1, and the settings are as follows:

```
Context | Name | Setting | Value
----------+---------+---------------------------+-----------------------------------
formation | primary | number_sync_standbys | 1
primary | node_1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_2)'
node | node_1 | candidate priority | 50
node | node_2 | candidate priority | 50
node | node_1 | replication quorum | true
node | node_2 | replication quorum | true
```

I would like to know, if this is expected and when will number_sync_standbys be adjusted