Switch back to default timeout for mac-arm64-rel-tests.

We're only testing arm64 binaries now and have additional capacity.

Bug: 1139038
Change-Id: Id1a5f9d03276f24173af2c42b5abd99db46d9fd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2557227Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830730}

infra/config/generated/cr-buildbucket.cfg

@@ -19045,7 +19045,7 @@ buckets {
         cmd: "recipes"
       }
       properties: "{\"$build/goma\":{\"use_luci_auth\":true},\"$kitchen\":{\"devshell\":true,\"git_auth\":true},\"$recipe_engine/isolated\":{\"server\":\"https://isolateserver.appspot.com\"},\"builder_group\":\"chromium.fyi\",\"recipe\":\"chromium\"}"
-      execution_timeout_secs: 21600
+      execution_timeout_secs: 10800
       build_numbers: YES
       service_account: "chromium-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
       experiments {

infra/config/subprojects/chromium/ci.star

@@ -4463,9 +4463,6 @@ ci.thin_tester(
         category = "mac",
         short_name = "a64",
     ),
-    # TODO(gbeaty) Once we have sufficient test capacity to not need to
-    # serialize tests, use the default execution_timout
-    execution_timeout = 6 * time.hour,
     tree_closing = False,
     triggered_by = [builder_name("mac-arm64-rel")],
 )