[roll] Roll fuchsia [build][idk] Use valico to validate atom metadata schema

Specify `use_valico = true` in `sdk_atom(). As described in the bug, the
existing validation mechanism is flawed. `sdk_molecule()` is already
using valico.

Fix a missing part of the sysroot schema that was found when switching.

Original-Bug: 42168969
Test: fx build //sdk:final_fuchsia_idk
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1257989
Original-Revision: cfae1a90168442db8b55fab7812713b8e8fc4f52
GitOrigin-RevId: d1d664eebc9dfc927c6a1995e890c083282e87e8
Change-Id: Icd7a46becb47e1d7f387fa6ea935a41229865081
diff --git a/stem b/stem
index 3a8f470..08981d9 100644
--- a/stem
+++ b/stem
@@ -8,7 +8,7 @@
              root=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="5144f17ebacacc684abc7fd155499d793044c659"
+             revision="cfae1a90168442db8b55fab7812713b8e8fc4f52"
              />
   </imports>
 </manifest>