project.config: restrict submission to internal branches

Starting with Go 1.16, a new name for release branches will be used.
The same access controls that limit submission on release branches
to the release-managers group need to apply to the upcoming internal
branches too.

For golang.org/issue/36882.

Change-Id: Id6b34be93e05e15a409a83450a11829364cb6d33
Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/283262
Reviewed-by: DO NOT USE <dmitshur@google.com>

project.config

diff --git a/project.config b/project.config
index b89886e..7d3416d 100644
--- a/project.config
+++ b/project.config
@@ -88,7 +88,7 @@
 [commitmessage]
 	maxSubjectLength = 1000
 	maxLineLength = 1000
-[access "^refs/heads/release-branch.+"]
+[access "^refs/heads/(release|internal)-branch.+"]
 	exclusiveGroupPermissions = submit
 	submit = group release-managers
 [access "^refs/heads/release-branch(.+)-security$"]