[ArrayManager] TST: enable JSON tests (except for table schema)
xref https://github.com/pandas-dev/pandas/issues/39146

This already enables most of the JSON tests (it are only the table schema tests that are segfaulting). Those are mostly working because the JSON writer falls back to using `df.values`. This only gives some errors with datetime formatting, for which one test is skipped (and this will then be fixed by letting the JSON code work column-by-column)
The failure is a flaky ResourceWarning error