[sdk-platform-java] Some downstream native configs initialize JUnit classes at build time in production

From https://github.com/googleapis/sdk-platform-java/pull/3674

Some libraries mark JUnit classes for initialization at build time in its _production_ native properties file.

For example: https://github.com/googleapis/java-spanner-jdbc/blob/fa65ead20018c083749bb1bd1cc1993f48745ef9/src/main/resources/META-INF/native-image/com.google.cloud/google-cloud-spanner-jdbc/native-image.properties#L15

I tried moving it to a test-only config file (`src/test/resources...`) but the image creation would fail asking to specify the JUnit classes to be initialized at runtime.