Limit batch size for internal bot

We have an explicit triggering_policy for this to limit
to one concurrent run, but had not updated this with a batch size

Change-Id: I2fd810a0d4dd33dbe2b8f7c79eef735f462913db
diff --git a/infra/config/global/main.star b/infra/config/global/main.star
index 61677b9..303dffe 100755
--- a/infra/config/global/main.star
+++ b/infra/config/global/main.star
@@ -305,7 +305,8 @@
         dimensions = get_dimensions(internal=True),
         triggering_policy = scheduler.policy(
             kind = scheduler.GREEDY_BATCHING_KIND,
-            max_concurrent_invocations = 1
+            max_concurrent_invocations = 1,
+            max_batch_size = 1
         ),
         priority = 25,
         properties = {