[infra] Run experimental mac builder less often to conserve capacity

Change-Id: I84e52d66cdf7c24b347614babe584d89abea9aee
Reviewed-on: https://dart-review.googlesource.com/72840
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: William Hesse <whesse@google.com>
diff --git a/tools/infra/config/cq.cfg b/tools/infra/config/cq.cfg
index f893762..758bbb7 100644
--- a/tools/infra/config/cq.cfg
+++ b/tools/infra/config/cq.cfg
@@ -31,7 +31,7 @@
       builders { name: "vm-canary-linux-debug-try" }
       builders { name: "vm-kernel-linux-release-simdbc64-try" }
       builders { name: "vm-kernel-linux-release-x64-try" }
-      builders { name: "vm-kernel-mac-release-x64-try" experiment_percentage: 100 }
+      builders { name: "vm-kernel-mac-release-x64-try" experiment_percentage: 5 }
       builders { name: "vm-linux-product-x64-try" }
       builders { name: "vm-linux-release-x64-try" }
       builders { name: "vm-mac-release-x64-try" }