Bug(v2): Having a non empty `yml` file in the directory provided to `sync` fails the sync with a confusing message

### Describe the Bug

To reproduce:
1. `echo "test: test" > cloudquery.yml`
2. `cloudquery sync "."`

See the error:
```basd
Loading specs from directory:  .
Error: no destinations found for source
```

### Expected Behavior

The error should say "`cloudquery.yml` is not a valid configuration file"

### CloudQuery Version

`cloudquery version 0.33.1-pre.0`
