[roll] Roll fuchsia [test] Move all users to new mock-mmio-reg-zxtest lib

See:
  https://fuchsia-review.googlesource.com/c/fuchsia/+/1029799

Original-Bug: b/328812587
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1030754
Original-Revision: a84116d0ccce5c7f8956fd6df9bb38760846dbc9
GitOrigin-RevId: d5309b870dea1f9fc7980902cfa3b95b879a7e0e
Change-Id: Iac408593150ca317c08259409d1603e962314dce
diff --git a/stem b/stem
index 97162d7..f142bc3 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="8ebf5592af427b204beaa96baeac0fe94cdd353c"/>
+             revision="a84116d0ccce5c7f8956fd6df9bb38760846dbc9"/>
   </projects>
   <hooks>
     <hook name="install-environment"