project.config: grant Forge Author Identity to approvers

This will allow approvers to create cherrypick CLs. See https://github.com/golang/go/issues/55841#issuecomment-1379347816.

Change-Id: I95dde41c842500ec7526ca2c1c78e16143ef70f1
Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/461799
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

project.config

diff --git a/project.config b/project.config
index bee211b..b408ee1 100644
--- a/project.config
+++ b/project.config
@@ -20,6 +20,7 @@
 	push = group Registered Users
 	pushMerge = group Registered Users
 [access "refs/heads/*"]
+	forgeAuthor = group approvers
 	forgeAuthor = group gerritbot
 	forgeAuthor = group may-forge-author-identity
 	forgeCommitter = group gerritbot