Specify encoding for AUTHORS file

Needed to resolve "UnicodeDecodeError" for Python 3 presubmit checks.

Bug: 1210746
Change-Id: If55190ffc9f99c671a84fe9b3539317e464639cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2904927
Commit-Queue: Dirk Pranke <dpranke@google.com>
Auto-Submit: Alan Screen <awscreen@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>

presubmit_canned_checks.py

@@ -128,7 +128,7 @@ def CheckAuthorizedAuthor(input_api, output_api, bot_allowlist=None):
       input_api.PresubmitLocalPath(), 'AUTHORS')
   valid_authors = (
       input_api.re.match(r'[^#]+\s+\<(.+?)\>\s*$', line)
-      for line in open(authors_path))
+      for line in open(authors_path, encoding="utf-8"))
   valid_authors = [item.group(1).lower() for item in valid_authors if item]
   if not any(input_api.fnmatch.fnmatch(author.lower(), valid)
              for valid in valid_authors):