chore(deps): update dependency pytest to v7 (#282)

Author: renovate-bot

bigquery-datatransfer/snippets/requirements-test.txt

@@ -1,4 +1,4 @@
 google-cloud-bigquery==2.32.0
 google-cloud-pubsub==2.9.0
-pytest==6.2.5
+pytest==7.0.0
 mock==4.0.3