Fix validation of manually generated configs

BUG=tint:693

Change-Id: I451b98883972b96b8320dbfeeabd66c947aba8bc
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51580
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Jamie Madill <jmadill@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>

infra/config/global/luci-milo.cfg

diff --git a/infra/config/global/luci-milo.cfg b/infra/config/global/luci-milo.cfg
index 159f726..2036d0e 100644
--- a/infra/config/global/luci-milo.cfg
+++ b/infra/config/global/luci-milo.cfg
@@ -1,6 +1,7 @@
 consoles: <
   id: "ci"
   name: "Tint CI Builders"
+  manifest_name: "REVISION"
   repo_url: "https://dawn.googlesource.com/tint"
   refs: "regexp:refs/heads/main"
   builders: <