Add google-truth to WEBRTC_ONLY_DEPS to unblock Chromium roll.

https://ci.chromium.org/ui/p/webrtc/builders/cron/Auto-roll%20-%20WebRTC%20DEPS/25338/overview

Change-Id: Ifc0a13b080843f5acde9188312bee9504811aadc
Bug: None
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/323901
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#40954}

PRESUBMIT.py

@@ -49,6 +49,7 @@ CPPLINT_EXCEPTIONS = [
 
 PYLINT_OLD_STYLE = [
     "PRESUBMIT.py",
+    "tools_webrtc/autoroller/roll_deps.py",
 ]
 
 # These filters will always be removed, even if the caller specifies a filter