Fixed ImportError issue with traffic_annotation/update_annotations_sheet.py

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8872768115210425728/+/steps/test_traffic_annotation_auditor/0/stdout

Change-Id: I71dc3b776a918a43ec389c070f050f345b64d79a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2340185Reviewed-by: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Commit-Queue: Mohamadou Bella Bah <bellabah@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795506}

tools/traffic_annotation/scripts/update_annotations_sheet.py.vpython

@@ -53,4 +53,9 @@ wheel: <
 wheel: <
   name: "infra/python/wheels/requests-py2_py3"
   version: "version:2.13.0"
+>
+
+wheel: <
+  name: "infra/python/wheels/enum34-py2"
+  version: "version:1.1.6"
 >
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