Enable "chromium.resultdb.result_sink" experiment on chromium ci builders at 50%

Bug: 1108016
Change-Id: Ic766443b0034b0d41cece5a4fdabbb95f47b9c94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2529970Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Chan Li <chanli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825907}

infra/config/lib/ci.star

@@ -396,9 +396,9 @@ def ci_builder(
     ]
     merged_resultdb_bigquery_exports.extend(resultdb_bigquery_exports or [])
 
-    # Enable "chromium.resultdb.result_sink" on ci builders at 10%.
+    # Enable "chromium.resultdb.result_sink" on ci builders at 50%.
     experiments = experiments or {}
-    experiments.setdefault("chromium.resultdb.result_sink", 10)
+    experiments.setdefault("chromium.resultdb.result_sink", 50)
 
     # Define the builder first so that any validation of luci.builder arguments
     # (e.g. bucket) occurs before we try to use it