`appenderRefs` in v1 properties files not handled correctly

Converting [this file](https://github.com/apache/logging-log4j2/blob/2.x/log4j-core-test/src/test/resources/log4j-rolling.properties) from `v1:properties` to `v2:xml` produces invalid configuration:

```shell
$ java -jar ~/Downloads/log4j-transform-cli.jar config-file convert -i v2:properties -o v2:xml log4j-core-test/src/test/resources/log4j-rolling.properties output.xml
```

```xml

```

This results in a runtime warning:

```
[junit] 2025-08-04T21:49:33.638Z main ERROR Root contains an invalid element or attribute "appenderRefs"
```

I assume that `rootLogger.appenderRefs=...` is valid Log4j2 properties config syntax, since it appears in Log4j2's test corpus as well as various Google search results ([example](https://coderanch.com/t/785028/java/log-creating-logging-file-console)).