[buildbucket] fix task force group name

TBR=iannucci@chromium.org

No-Try: true
Change-Id: Idbcf63650aac281cd3a98aed4a8c6cd453d78c72
Reviewed-on: https://chromium-review.googlesource.com/963293Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Nodir Turakulov <nodir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543174}

infra/config/global/cr-buildbucket.cfg

@@ -41,7 +41,7 @@ acl_sets {
   acls {
     # Allow task force to bump next build number.
     role: WRITER
-    group: "luci-task-force@google.com"
+    group: "google/luci-task-force@google.com"
   }
 }