Update WebRTC code version (2021-09-09T04:03:59).

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

Bug: None
Change-Id: If8e2d0d375ec6a636c77d0b602ed762f782c3ea0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/231625
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@{#34957}

call/version.cc

diff --git a/call/version.cc b/call/version.cc
index 3940f5b..b9a23ad 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 2021-09-08T04:04:58";
+const char* const kSourceTimestamp = "WebRTC source stamp 2021-09-09T04:03:59";
 
 void LoadWebRTCVersionInRegister() {
   // Using volatile to instruct the compiler to not optimize `p` away even