pubsub: small fixes for end-to-end tests
pubsub: small fixes for end-to-end tests

Fixing that some channels are never closed during tests.

Change-Id: Ife9ece48c7d3cf0a113c54130c93fae30d5acc7b
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/54870
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Alex Hong <3311379d571f0e1dc66d44c9732cbfa024b0fda6@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go