json schema inference can't handle null field turned into object field in subsequent rows

[kskalski]

Describe the bug
Such scenario produces
JsonError("Expected object json type, found: Any")

To Reproduce

    #[test]
    fn test_infer_from_null_then_object() {
        let data = r#"
            {"obj":null}
            {"obj":{"foo":1}}
        "#;
        let (inferred_schema, _) =
            infer_json_schema_from_seekable(Cursor::new(data), None).expect("infer");
    }

Expected behavior
Schema should be inferred and have struct data type for obj field

Additional context
arrow-rs master / v49.0.0

[tustvold]

label_issue.py automatically added labels {'arrow'} from #5216