Test updating schema after _get_subset_schema

`_get_subset_schema` was implemented when it wasn't possible to make changes to the Schema object, so it has few checks that the subset and original schema aren't tied to each other in a way that could be problematic if we mutate one of the schemas.

Since many Schema and Table Accessor operations rely on `_get_subset_schema`, it's important that no part of the schema returned by `_get_subset_schema` is tied to the original schema, so we should add a test that updates the original schema and the subset schema's tags, logical types, indices, metadata, and column descriptions.