Update last-release-sha in release config

This should remove extra commits from history release notes.

Author: matttrach

release-please-config.json

@@ -1,5 +1,6 @@
 {
   "bootstrap-sha": "ab77bd4030512387b04480079c38aa54f8590eb9",
+  "last-release-sha": "855669080db821c5e6697161048267e72a232f63",
   "release-as": "v14.0.0",
   "always-update": true,
   "commit-search-depth": 100,