Add protobuf-py2_py3 3.13.0 to .vpython.

Starting from https://webrtc-review.googlesource.com/c/src/+/194081,
WebRTC's protobuf are using version 3.13.0.1+ but when running on
bots, we see errors that are probably caused by a version mismatch, see
https://ci.chromium.org/p/webrtc/builders/perf/Perf%20Linux%20Trusty/4597.

This CL updates WebRTC's .vpython to use protobuf 3.13.0.

TBR=kwiberg@webrtc.org

No-Try: True
Bug: None
Change-Id: I6bc5e71bacc67dbd9299a9588ddf826778451949
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/194143
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Andrey Logvin <landrey@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32642}

.vpython

@@ -66,6 +66,10 @@ wheel: <
   name: "infra/python/wheels/mock-py2_py3"
   version: "version:2.0.0"
 >
+wheel: <
+  name: "infra/python/wheels/protobuf-py2_py3"
+  version: "version:3.13.0"
+>
 wheel: <
   name: "infra/python/wheels/requests-py2_py3"
   version: "version:2.13.0"