[resultdb] enable gtest_local experiment on ci builders

There are only 3 builders, running local gtests.
- chromium.fyi.Win 10 Fast Ring
- chromium.linux.Cast Audio Linux
- chromium.linux.Cast Linux

The LocalGTest steps with rdb on the FYI builder have been running
successfully, and the two other builders have been tested with
LED builds.

Bug: 1084332
Change-Id: I17e39d855b4d306ccb68b02cfb05626cc0a030d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618522
Commit-Queue: Scott Lee <ddoman@chromium.org>
Reviewed-by: Chan Li <chanli@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841687}

infra/config/lib/ci.star

@@ -96,6 +96,7 @@ def ci_builder(
     experiments = experiments or {}
     experiments.setdefault("chromium.resultdb.result_sink", 100)
     experiments.setdefault("chromium.resultdb.result_sink.junit_tests", 100)
+    experiments.setdefault("chromium.resultdb.result_sink.gtests_local", 100)
 
     # Define the builder first so that any validation of luci.builder arguments
     # (e.g. bucket) occurs before we try to use it
@@ -368,9 +369,6 @@ def fyi_builder(
         builder_group = "chromium.fyi",
         execution_timeout = execution_timeout,
         goma_backend = goma_backend,
-        experiments = {
-            "chromium.resultdb.result_sink.gtests_local": 30,
-        },
         **kwargs
     )