[roll] Roll fuchsia [starnix] Remove async code from tests

By using fdio in synchronous contexts, we can eliminate the need for an
executor in tests.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/663922
Original-Revision: a8ea8b25144a8fda6228a2a4d80629a51bb45a76
GitOrigin-RevId: b30d8885ad55b53e0d82939b0b4ed65a32378e46
Change-Id: Ic26ccf2f9cf090d67167095a49eeb05a9b49fd83
diff --git a/stem b/stem
index 2baa4d6..d2d37d8 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="5f4668fc913fa728839e5b838304dd5f6602f381"/>
+             revision="a8ea8b25144a8fda6228a2a4d80629a51bb45a76"/>
   </projects>
   <hooks>
     <hook name="install-environment"