all: release v0.55.0

This commit will be tagged v0.55.0.

Change-Id: I36e18f8192245f1a8b367839b73d8ff6d8908c53
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/53310
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Noah Dietz <ndietz@google.com>
diff --git a/CHANGES.md b/CHANGES.md
index 3fa4900..8c0d7d5 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,9 @@
 # Changes
 
+## v0.55.0
+
+- Various updates to autogenerated clients.
+
 ## v0.54.0
 
 - all: