message: proto_sync: improve error message.
  It was previously pointing at proto_sync.py, which is misleading, it's
  necessary to run the full tools/proto_format.sh for a proto fix.
diff: @@ -52,7 +52,8 @@ class RequiresReformatError(ProtoSyncError):
  def __init__(self, message):
  super(RequiresReformatError, self).__init__(
  - '%s; either run ./ci/do_ci.sh fix_format or %s fix to reformat.\n' % (message, sys.argv[0]))
  + '%s; either run ./ci/do_ci.sh fix_format or ./tools/proto_format.sh fix to reformat.\n' %
  + message)
  def LabelPaths(label, src_suffix):
  