[roll] Roll fuchsia [fidl][llcpp] Fix use-after-free in server test

And add a comment blurb since this test was very confusing to grok.

Multiply: fidl_llcpp_gen_api_tests
Original-Fixed: 84839
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/582842
Original-Revision: 231d7219fbf13a745837be420679708d8ba0c6f7
GitOrigin-RevId: 1db9d2ba4cf32e28eb0abcb4b823becae5392f3f
Change-Id: I7e02749084c290b2427b458441440a815833ca7e
diff --git a/stem b/stem
index 05e9f02..ec7ab09 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="c4c35f076993fba9db60f9ec9b4e66dc07038786"/>
+             revision="231d7219fbf13a745837be420679708d8ba0c6f7"/>
   </projects>
   <hooks>
     <hook name="install-environment"