chore: release 1.26.0 (#689)

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
diff --git a/setup.py b/setup.py
index ba72c3c..2f16e44 100644
--- a/setup.py
+++ b/setup.py
@@ -34,7 +34,7 @@
 with io.open("README.rst", "r") as fh:
     long_description = fh.read()
 
-version = "1.25.0"
+version = "1.26.0"
 
 setup(
     name="google-auth",