Infra: Use Python 3 for the Tint recipe

BUG=chromium:1256440

Change-Id: If1983c22da65ef14f21c992edf89face29f7a388
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/68020
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
diff --git a/infra/config/global/main.star b/infra/config/global/main.star
index faa43d4..263c278 100755
--- a/infra/config/global/main.star
+++ b/infra/config/global/main.star
@@ -10,7 +10,10 @@
 
 # Enable realms experiment.
 lucicfg.enable_experiment("crbug.com/1085650")
-luci.builder.defaults.experiments.set({"luci.use_realms": 100})
+luci.builder.defaults.experiments.set({
+    "luci.use_realms": 100,
+    "luci.recipes.use_python3": 100,
+})
 
 lucicfg.config(fail_on_warnings = True)