Make PipeWire 0.3 default version

PipeWire 0.2 is quite old and the new version of PipeWire should be now
available everywhere where needed, including sysroot images.

Bug: chromium:1146942
Change-Id: I04c8b3747f3535eb1b22294c96119f1c9c7e68d2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/204300
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33160}

webrtc.gni

@@ -118,8 +118,8 @@ declare_args() {
   rtc_link_pipewire = false
 
   # Set this to use certain PipeWire version
-  # Currently we support PipeWire 0.2 (default) and PipeWire 0.3
-  rtc_pipewire_version = "0.2"
+  # Currently WebRTC supports PipeWire 0.2 and PipeWire 0.3 (default)
+  rtc_pipewire_version = "0.3"
 
   # Enable to use the Mozilla internal settings.
   build_with_mozilla = false