Add 'requests' to .vpython.

This is needed since after [1], "requests" is imported by result_sink.py
but there are no explicit dependencies to configure the sys.path to
the requests module.

This CL applies the same configuration Chromium has, see [2].

[1] - https://chromium-review.googlesource.com/c/chromium/src/+/2365216
[2] - https://source.chromium.org/chromium/chromium/src/+/master:.vpython;l=285-288;drc=e6df1447adea859ee8161feba5f803903ff55fee

TBR=tommi@webrtc.org

No-Try: True
Bug: chromium:1104245
Change-Id: I76fd8b183907fc923db633017914429d52003d4a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/183762
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32059}
diff --git a/.vpython b/.vpython
index fb75db5..e8dc8e2 100644
--- a/.vpython
+++ b/.vpython
@@ -66,3 +66,7 @@
   name: "infra/python/wheels/mock-py2_py3"
   version: "version:2.0.0"
 >
+wheel: <
+  name: "infra/python/wheels/requests-py2_py3"
+  version: "version:2.13.0"
+>