Update WebRTC code version (2021-12-15T04:02:29).

Bug: None
Change-Id: I0996640eb68046f53d18c40d73d6959b0642f3f1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/241500
Bot-Commit: webrtc-version-updater@webrtc-ci.iam.gserviceaccount.com <webrtc-version-updater@webrtc-ci.iam.gserviceaccount.com>
Commit-Queue: webrtc-version-updater@webrtc-ci.iam.gserviceaccount.com <webrtc-version-updater@webrtc-ci.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#35538}

call/version.cc

diff --git a/call/version.cc b/call/version.cc
index 1f6d1b6..b3d740f 100644
--- a/call/version.cc
+++ b/call/version.cc
@@ -13,7 +13,7 @@
 namespace webrtc {
 
 // The timestamp is always in UTC.
-const char* const kSourceTimestamp = "WebRTC source stamp 2021-12-14T04:04:40";
+const char* const kSourceTimestamp = "WebRTC source stamp 2021-12-15T04:02:29";
 
 void LoadWebRTCVersionInRegister() {
   // Using volatile to instruct the compiler to not optimize `p` away even