Set cores to 2 for internal bot.

This was set for the new setup here:
https://chrome-internal-review.googlesource.com/c/infradata/config/+/3125502

Change-Id: Ia6750a511521defeeb30b7d77ed5f4f702af34ac
diff --git a/infra/config/global/cr-buildbucket.cfg b/infra/config/global/cr-buildbucket.cfg
index 87562ad..afa5f60 100644
--- a/infra/config/global/cr-buildbucket.cfg
+++ b/infra/config/global/cr-buildbucket.cfg
@@ -29,6 +29,7 @@
 builder_mixins {
   name: "internal"
   dimensions: "internal:true"
+  dimensions: "cores:2"
 }
 
 builder_mixins {