Change coverage_report.py shabang to run vpython3.

Bug: pdfium:1674
Change-Id: Ic0dbcad834aeb2b804b81628233724f631bcdac1
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/91270
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/testing/tools/coverage/coverage_report.py b/testing/tools/coverage/coverage_report.py
index 32016fc..c07a082 100755
--- a/testing/tools/coverage/coverage_report.py
+++ b/testing/tools/coverage/coverage_report.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env vpython
+#!/usr/bin/env vpython3
 # Copyright 2017 The PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.