[roll] Roll fuchsia [kernel][ktl] Define _LIBCPP_PSTL_CPU_BACKEND_SERIAL

Original-Bug: 127108
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/863298
Original-Revision: 0b4731805f72538ae523d4a8627cdac792105897
GitOrigin-RevId: 5390ef286da1900e4e345b177cfafe6ad2b1a82d
Change-Id: Ie0b89008f83dbb9d3fe49d06c406342981d291ed
diff --git a/stem b/stem
index 54b62e2..badc1d4 100644
--- a/stem
+++ b/stem
@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="79260dabd5971a66ed7646e060d1c35193f64c22"/>
+             revision="0b4731805f72538ae523d4a8627cdac792105897"/>
   </projects>
   <hooks>
     <hook name="install-environment"