[Docker] Synapse generates `log.config` in `/data/conf.d` and then prints (harmless) message saying it is ignoring it due to lack of YAML extension

### Description

Synapse says:

```
Generating log config file /data/conf.d/log.config which will log to /homeserver.log
```

and it says a few seconds later:

```
Found file in config directory that does not end in '.yaml': '/data/conf.d/log.config'. IGNORING.
```

### Steps to reproduce

- do not have log file
- start Synapse

### Synapse Version

1.100.0

### Installation Method

Docker (matrixdotorg/synapse)

### Database

PostgreSQL

### Workers

Single process

### Platform

Debian stable

### Configuration

Pretty much default config, presende disabled, nothing special

### Relevant log output

See above.

### Anything else that would be useful to know?

nope