all: release v0.12.0

Change-Id: I27ca8c8fdd3770a5e1f0ed521ba04cefd77359a0
Reviewed-on: https://code-review.googlesource.com/c/google-api-go-client/+/47511
Reviewed-by: Noah Dietz <ndietz@google.com>

CHANGES.md

diff --git a/CHANGES.md b/CHANGES.md
index 22c8c61..c40dafc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,7 @@
+# v0.12.0
+
+- Various updates to autogenerated clients.
+
 # v0.11.0
 
 - Various updates to autogenerated clients.