checkout: Formatting fix

Change-Id: I0c6459c1b17665158e5328d36b72d73e9e4b9f29
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/103680
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Oliver Newman <olivernewman@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/recipe_modules/checkout/test_api.py b/recipe_modules/checkout/test_api.py
index 5b4c131..4fa2822 100644
--- a/recipe_modules/checkout/test_api.py
+++ b/recipe_modules/checkout/test_api.py
@@ -238,7 +238,7 @@
         self,
         *submodules,
         prefix='checkout pigweed.',
-        checkout_root='[START_DIR]/checkout'
+        checkout_root='[START_DIR]/checkout',
     ):
         sub_data = {sub['path']: sub for sub in submodules}