infra: linux-goma-rbe-staging-rel experiment: 5% -> 10%

Previously, it was reduced from 10% to 5% due to machine overload:
http://crrev.com/c/1235273

Now we have more machines added in https://crrev.com/i/703404.
(Disregard the incorrect CL name)

BUG=855319

Change-Id: I5dbce569f1d4cf3e8fd45fbcd9068124351dd12c
Reviewed-on: https://chromium-review.googlesource.com/c/1331288Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Simon Que <sque@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607157}

infra/config/branch/cq.cfg

@@ -118,7 +118,7 @@ verifiers {
       # https://crbug.com/855319
       builders {
         name: "linux-goma-rbe-staging-rel"
-        experiment_percentage: 5
+        experiment_percentage: 10
       }
       builders { name: "linux-jumbo-rel" }
       builders {