[roll] Roll fuchsia [rbe] credentials helper no longer experimental

Rename to non-experimental options.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1131412
Original-Revision: 992facdf4df78d3dd2e6fe42f486cb3a025d2a9a
GitOrigin-RevId: 5364724486014c94daa03abef05a6aae3d2b621e
Change-Id: I476585d8332396c5cce09de72a9eb57d5cb3d999
diff --git a/stem b/stem
index 5bcdf7e..684a93b 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="291bcd6646867b6ab965673d0cc73895391797ee"/>
+             revision="992facdf4df78d3dd2e6fe42f486cb3a025d2a9a"/>
   </projects>
   <hooks>
     <hook name="install-environment"