[roll] Roll fuchsia [sysmem] add thread role for fuchsia.sysmem.loop

This thread serves Sysmem requests which can be latency sensitive, see
bug for details. Assign a scheduler role to it so we can add a profile.

Original-Original-Bug: 525134374
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1699838
Original-Original-Revision: 420e681ef1afa62a95089494d7aaf27a2b69df5c
GitOrigin-RevId: a4a74887c848a314aca594ff28130959c63e57aa
Change-Id: I57c162f4c1e6e96868a1801e1fa037883b5bcf26
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1713412
Cr-Commit-Position: refs/heads/main@{#197214}

stem

diff --git a/stem b/stem
index 4244306..175d8e9 100644
--- a/stem
+++ b/stem
@@ -8,6 +8,6 @@
             manifest="manifests/platform"
             root=""
             remote="https://fuchsia.googlesource.com/fuchsia"
-            revision="1b06254ce9e7cbb80873890b6a61067c42ae5b03"/>
+            revision="420e681ef1afa62a95089494d7aaf27a2b69df5c"/>
   </imports>
 </manifest>