Override use_cxx23 to false.

WebRTC, compared to Chromium will switch to C++23 at a later time.

But as mentioned in the WebRTC style guide [1], WebRTC allows the subset
of C++20 that is also valid C++23:

WebRTC is written in C++20, but with some restrictions:

* We only allow the subset of C++20 (language and library) that is not banned by
  Chromium;
* We only allow the subset of C++20 that is also valid C++23; otherwise, users
  would not be able to compile WebRTC in C++23 mode.

[1] - third_party/webrtc/g3doc/style-guide.md

Bug: chromium:388070065
Change-Id: I50b6b46f4e90f1ba3dea15d24b29aa05e01d05f4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/428321
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46294}