[Release] arrow-java-root-18.3.0-source-release.zip includes JNI binaries

### Describe the bug, including details regarding any error messages, version, and platform.

This is not a release blocker.

https://github.com/apache/arrow-java/releases/download/v18.3.0-rc2/arrow-java-root-18.3.0-source-release.zip

JNI binaries are large. Can we remove them from `source-release.zip`?

```console
$ LANG=C du -hsc arrow-java-root-18.3.0/jni/*
236K arrow-java-root-18.3.0/jni/arrow_cdata_jni/
272M arrow-java-root-18.3.0/jni/arrow_dataset_jni/
156M arrow-java-root-18.3.0/jni/arrow_orc_jni/
444M arrow-java-root-18.3.0/jni/gandiva_jni/
871M total
```

`source-release.zip` also has `testing/`. It's not so large but should we remove it? Or should we keep it?

```console
$ LANG=C du -hsc arrow-java-root-18.3.0/testing
8.8M arrow-java-root-18.3.0/testing
8.8M total
```

Comienza con el source-release.zip de v18.3.0-rc2 e inspecciona cómo se ensamblan sus directorios jni/ y testing/. Determina si los binarios JNI y testing/ deben estar en el archivo fuente y, a continuación, verifica que el archivo resultante ya no incluya los binarios no deseados y siga siendo una versión fuente válida.

Escrito por el modelo de indexación a partir del texto del issue.