chore: release pubsub 1.12.0 (#4266)

🤖 I have created a release \*beep\* \*boop\*
---
## [1.12.0](https://www.github.com/googleapis/google-cloud-go/compare/pubsub/v1.11.0...pubsub/v1.12.0) (2021-06-23)


### Features

* **pubsub/pstest:** add channel to support user-defined publish responses ([#4251](https://www.github.com/googleapis/google-cloud-go/issues/4251)) ([e1304f4](https://www.github.com/googleapis/google-cloud-go/commit/e1304f435fed4a767f4a652f32f1386979ff794f))


### Bug Fixes

* **pubsub:** fix memory leak issue in publish scheduler ([#4282](https://www.github.com/googleapis/google-cloud-go/issues/4282)) ([22ffc18](https://www.github.com/googleapis/google-cloud-go/commit/22ffc18e522c0f943db57f8c943e7356067bedfd))

This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

pubsub/CHANGES.md

@@ -1,5 +1,17 @@
 # Changes
 
+## [1.12.0](https://www.github.com/googleapis/google-cloud-go/compare/pubsub/v1.11.0...pubsub/v1.12.0) (2021-06-23)
+
+
+### Features
+
+* **pubsub/pstest:** add channel to support user-defined publish responses ([#4251](https://www.github.com/googleapis/google-cloud-go/issues/4251)) ([e1304f4](https://www.github.com/googleapis/google-cloud-go/commit/e1304f435fed4a767f4a652f32f1386979ff794f))
+
+
+### Bug Fixes
+
+* **pubsub:** fix memory leak issue in publish scheduler ([#4282](https://www.github.com/googleapis/google-cloud-go/issues/4282)) ([22ffc18](https://www.github.com/googleapis/google-cloud-go/commit/22ffc18e522c0f943db57f8c943e7356067bedfd))
+
 ## [1.11.0](https://www.github.com/googleapis/google-cloud-go/compare/pubsub/v1.10.3...pubsub/v1.11.0) (2021-05-27)