Using --raw-command with stderr

I'm using a CI tool that acts as a wrapper for the Go command and emits the results via stderr rather than stdout. I've tried various ways of incorporating this into the raw command, along the lines of:

```shell
gotestsum --junitfile test.xml --ignore-non-json-output-lines --raw-command -- jfrog rt go test -v -json ./... 2>&1
```

but am always ending up with an empty output (and stderr appearing in the console). Is there a recommended way to parse stderr using gotestsum?

Start by tracing how gotestsum handles --raw-command and separates stdout from stderr, then reproduce the reported jfrog rt go test command with stderr redirected. Done means stderr-emitted Go test JSON is parsed correctly and the requested JUnit file is produced without leaving stderr only in the console.

Written by the indexing model from the issue text.