chore: release 2.2.0 (#872)

:robot: I have created a release \*beep\* \*boop\*
---
## [2.2.0](https://www.github.com/googleapis/google-auth-library-python/compare/v2.1.0...v2.2.0) (2021-09-21)


### Features

* add support for workforce pool credentials ([#868](https://www.github.com/googleapis/google-auth-library-python/issues/868)) ([993bab2](https://www.github.com/googleapis/google-auth-library-python/commit/993bab2aaacf3034e09d9f0f25d36c0e815d3a29))
---


This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).
diff --git a/google/auth/version.py b/google/auth/version.py
index a02dc8a..b423306 100644
--- a/google/auth/version.py
+++ b/google/auth/version.py
@@ -12,4 +12,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "2.1.0"
+__version__ = "2.2.0"