chore: release 2.6.0 (googleapis#428)

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

chore: release 2.5.0 (googleapis#412)

🤖 I have created a release \*beep\* \*boop\*
---
## [2.5.0](https://www.github.com/googleapis/python-pubsub/compare/v2.4.2...v2.5.0) (2021-05-18)


### Features

* make publish futures compatible with concurrent.futures.as_completed() ([googleapis#397](https://www.github.com/googleapis/python-pubsub/issues/397)) ([e29a2c0](https://www.github.com/googleapis/python-pubsub/commit/e29a2c0ac6c5d2ebf2311646e552a02f184cfedc))


### Bug Fixes

* scheduler errors when executor in shutdown ([googleapis#399](https://www.github.com/googleapis/python-pubsub/issues/399)) ([39a83d3](https://www.github.com/googleapis/python-pubsub/commit/39a83d3eef196e88478ad8362201a2ab12e9f681))
---


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

chore: release v2.4.2 (googleapis#409)

chore: release 2.4.1 (googleapis#347)

* chore: release 2.4.1

* Cleanup release notes.

* Update CHANGELOG.md

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

chore: release v2.4.0 (googleapis#296)

chore: release 2.3.0 (googleapis#283)

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

chore: release 2.2.0 (googleapis#234)

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

chore: release v2.1.0 (googleapis#204)

chore: Release v2.0.0 (googleapis#189)

* chore: release v2.0.0

* Add compatibility notice to 1.7.0 release notes.

* Fix typo in pull request URL in CHANGELOG.

chore: release v1.7.0 (googleapis#154)