GCS: HTTP error code 308 retries during upload. Previously, it would only...

GCS: HTTP error code 308 retries during upload. Previously, it would only permit 308 when getting the status of an upload.

This matches the behavior of the official library:
https://github.com/google/apitools/blob/master/apitools/base/py/transfer.py#L925

And the general description here:
https://cloud.google.com/storage/docs/json_api/v1/how-tos/resumable-upload

PiperOrigin-RevId: 187400843