OUTPUT_DIR variable in sdxl_env.sh is ignored


If you configure this:
```
### sdxl_env.sh
# Location of training data.
export BASE_DIR="/workspace/SimpleTuner/"
export INSTANCE_DIR="${BASE_DIR}/input/"
export OUTPUT_DIR="${BASE_DIR}/models"
```

Model is saved in :
`/notebooks/datasets/models/ptx0-xltest/`

^ Seems this path was hardcoded.