Fix byte string concat error in _HandleAUTH()

This fixes https://console.cloud.google.com/errors/CMebxsbZ1PzK8gE?time=PT1H&refresh=auto&project=chromium-swarm

Bug: 1198820
Change-Id: I88498d61a544b1107f0c7a138aae0900e4488e4a
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/python-adb/+/2943853
Auto-Submit: Junji Watanabe <jwata@google.com>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
1 file changed