[roll] Roll fuchsia [ktl] Add is_unsigned{,_v} to type_traits

This is useful for type enforcement, and is clearer than negating
is_signed{,_v}.

Original-Bug: 95763
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/672162
Original-Revision: 6e5090bc0d8329c50cf66115c75d43975e43e419
GitOrigin-RevId: 44b89bac0c23497403c73c9fdfb653b79e636361
Change-Id: Ib083c05ace8ca06872faa3ed9561381980cce42f

stem

diff --git a/stem b/stem
index 4f7ea90..186ced9 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="f0c9933802f3c9b47ba43b9319594ba7097ba1fc"/>
+             revision="6e5090bc0d8329c50cf66115c75d43975e43e419"/>
   </projects>
   <hooks>
     <hook name="install-environment"