[roll] Roll fuchsia [assembly] Default partitions has R slot

This fixes a build failure for core.qemu-arm64, which only happened
in CI.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1245586
Original-Revision: 88c88b219056f24bc31397feab8a2c38f8a0bc29
GitOrigin-RevId: 712fcf48baac88d6e725ff0aa891494609140b73
Change-Id: Icf9784c7656f6d7cf8ec7d2c2adb9b2463aa29f2
diff --git a/stem b/stem
index 7aa3c86..1fbeaf8 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="6453125b88f7d321e7a515a19be26be0adf424ff"
+             revision="88c88b219056f24bc31397feab8a2c38f8a0bc29"
              />
   </projects>
   <hooks>