chore: release 1.21.2 (#601)

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
diff --git a/setup.py b/setup.py
index c1218db..ea43594 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,7 @@
 with io.open("README.rst", "r") as fh:
     long_description = fh.read()
 
-version = "1.21.1"
+version = "1.21.2"
 
 setup(
     name="google-auth",