[Variant] `test_json_to_variant_object_very_large` takes over 20s

[alamb]

Describe the bug

        PASS [  20.847s] parquet-variant::test_json_to_variant test_json_to_variant_object_very_large

To Reproduce
cargo test -p parquet-variant

Expected behavior
I expect the test to be faster (ideally take less than 1 sec)

Additional context
The test came in as part of this PR from @harshmotw-db :

• [VARIANT] Add support for the json_to_variant API #7783

[alamb]

label_issue.py automatically added labels {'parquet'} from #7878