[Failing Test]: BigQuery load and copy load exception tests failing with new GCS client

### What happened?

The apitools-generated StorageV1 client has been replaced with the [GCS client](https://github.com/googleapis/python-storage). Unfortunately the mocking for test_load_job_exception and test_copy_load_job_exception in bigquery_test.py targets StorageV1's ObjectsService, causing those tests to now fail. Since the new client doesn't have an ObjectsService or a clear analog to it, a new mocking target is not obvious.

### Issue Failure

Failure: Test is continually failing

### Issue Priority

Priority: 2 (backlog / disabled test but we think the product is healthy)

### Issue Components

- [X] Component: Python SDK
- [ ] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner