Raise linux_chromium_ozone_compile_ng cq experiment from 10% to 50%

Bot is stable over the past months.
BUG=694033

Change-Id: I2f383da545eb39c4745a7cb18e35473f7aa62300
Reviewed-on: https://chromium-review.googlesource.com/793472Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#531503}

infra/config/cq.cfg

@@ -94,7 +94,7 @@ verifiers {
       }
       builders {
         name: "linux_chromium_ozone_compile_only_ng"
-        experiment_percentage: 10
+        experiment_percentage: 50
       }
       builders {
         name: "linux_chromium_compile_dbg_ng"