PubSubBigQueryIT.test_file_loads fails on Dataflow Runner

[damccorm]

The IT test - PubSubBigQueryIT fails on Dataflow Runner.
https://github.com/apache/beam/blob/master/sdks/python/apache_beam/io/gcp/bigquery_test.py#L833-L838

More context: #9427

Imported from Jira BEAM-8578. Original Jira may contain additional context.
Reported by: ttanay.