Add explicit path for infra in infra_superproject gclient config.

Recipe-Nontrivial-Roll: infra
Bug:1415507
Change-Id: Ic6973c4f0c9fa011549d44a89205a0731c3ff944
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4566110
Reviewed-by: Gavin Mak <gavinmak@google.com>
Auto-Submit: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>

recipes/recipe_modules/gclient/config.py

@@ -301,7 +301,8 @@ def infra_superproject(c):
       'https://chromium.googlesource.com/infra/luci/luci-go':
       ('infra/go/src/go.chromium.org/luci', 'HEAD'),
       'https://chromium.googlesource.com/infra/luci/recipes-py':
-      ('infra/recipes-py', 'HEAD')
+      ('infra/recipes-py', 'HEAD'),
+      'https://chromium.googlesource.com/infra/infra': ('infra', None)
   })