project.config: lock down go1.21 branch for release.

Change-Id: Ie0828f4ac6290b79f1e8e6be0a3c969448932d02
Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/516177
Reviewed-by: Heschi Kreinick <heschi@google.com>
1 file changed
tree: 764ef3b290406c9363ee5f9af7bd1b38e6d9f385
  1. buildbucket.config
  2. groups
  3. project.config