Reduce traffic to mac-coverage-rel from 10% to 8%

Observed rise in pending build times http://shortn/_wl495QJZSE

Bug: 1024915
Change-Id: Ie15cbaf6e0a52f489d77189b020203b4db1dc279
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405035
Auto-Submit: Prakhar Asthana <pasthana@google.com>
Commit-Queue: Erik Staab <estaab@chromium.org>
Reviewed-by: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806366}

infra/config/generated/commit-queue.cfg

@@ -1259,7 +1259,7 @@ config_groups {
       }
       builders {
         name: "chromium/try/mac-coverage-rel"
-        experiment_percentage: 10
+        experiment_percentage: 8
         location_regexp: ".*"
         location_regexp_exclude: ".+/[+]/docs/.+"
         location_regexp_exclude: ".+/[+]/infra/config/.+"

infra/config/generated/cq-builders.md

@@ -367,5 +367,5 @@ as required builders.
   * [`//services/tracing/.+`](https://cs.chromium.org/chromium/src/services/tracing/)
 
 * [mac-coverage-rel](https://ci.chromium.org/p/chromium/builders/try/mac-coverage-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+mac-coverage-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+mac-coverage-rel))
-  * Experiment percentage: 10
+  * Experiment percentage: 8
 

infra/config/subprojects/chromium/try.star

@@ -1092,7 +1092,7 @@ try_.chromium_mac_builder(
     builderless = False,
     use_clang_coverage = True,
     goma_jobs = goma.jobs.J150,
-    tryjob = try_.job(experiment_percentage = 10),
+    tryjob = try_.job(experiment_percentage = 8),
 )
 
 try_.chromium_mac_builder(