[Go][Integration] Go JSON producer generates incorrect nullable flag for nested types

It seems that when generating JSON integration data for a nested type, e.g.
"list(int32)", the list's nullable flag is also inherited by child fields. This is wrong, because child fields have independent nullable flags, e.g. you may have:

• "list(field("ints", int32, nullable=True), nullable=True)"
• "list(field("ints", int32, nullable=False), nullable=True)"
• "list(field("ints", int32, nullable=True), nullable=False)"
• "list(field("ints", int32, nullable=False), nullable=False)"