Log Message:
py-stripe: updated to 8.4.0

8.4.0 - 2024-02-22
* Update generated code
  - Add `InvoiceLineItem.modify` method.
* Add TaxIds API
  * Add support for `create`, `retrieve`, `delete`, and `list` methods on \ 
resource `TaxId`
  * The `instance_url` function on resource `TaxId` now returns the top-level \ 
`/v1/tax_ids/{id}` path instead of the `/v1/customers/{customer}/tax_ids/{id}` \ 
path.
* Remove http client base
* Testing: unify http client mock