Update WebRTC code version (2021-09-21T04:02:15).

TBR=webrtc-version-updater@webrtc-ci.iam.gserviceaccount.com,mbonadei@webrtc.org

Bug: None
Change-Id: I70cc13d8235696205e375cdc52869c2ceac3f078
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/232583
Reviewed-by: 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@{#35046}
diff --git a/call/version.cc b/call/version.cc
index 576fbee..ba18b2c 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 2021-09-19T04:02:28";
+const char* const kSourceTimestamp = "WebRTC source stamp 2021-09-21T04:02:15";
 
 void LoadWebRTCVersionInRegister() {
   // Using volatile to instruct the compiler to not optimize `p` away even