Enable use_python3 experiment for luci-config builder.

This builder is required to run on py3, because an upstream
change to use the git_checkout module instead of git, will
fail if builds are run on py2.

Bug:102383
Change-Id: I72c8d8f13b95637a32746d9395c93ed8994118b3
Reviewed-on: https://flutter-review.googlesource.com/c/infra/+/29540
Reviewed-by: Casey Hillers <chillers@google.com>
Reviewed-by: Oliver Newman <olivernewman@google.com>
Commit-Queue: Yusuf Mohsinally <mohsinally@google.com>
diff --git a/config/generated/flutter/luci/cr-buildbucket.cfg b/config/generated/flutter/luci/cr-buildbucket.cfg
index 545ce44..d1e1e54 100644
--- a/config/generated/flutter/luci/cr-buildbucket.cfg
+++ b/config/generated/flutter/luci/cr-buildbucket.cfg
@@ -227562,6 +227562,10 @@
       execution_timeout_secs: 600
       service_account: "flutter-try-builder@chops-service-accounts.iam.gserviceaccount.com"
       task_template_canary_percentage {}
+      experiments {
+        key: "luci.recipes.use_python3"
+        value: 100
+      }
     }
     builders {
       name: "recipes-unittest-only"
diff --git a/config/infra_config.star b/config/infra_config.star
index 0e3c63a..35015c9 100644
--- a/config/infra_config.star
+++ b/config/infra_config.star
@@ -46,6 +46,7 @@
         ],
         properties = {},
         service_account = accounts.FLUTTER_TRY,
+        experiments = {"luci.recipes.use_python3": 100},
     )
 
 infra_config = struct(setup = _setup)