[roll] Roll fuchsia [fx-worktree] Run jiri worktree sync after checkout

When fx worktree add <name> --sync is run, syncing
before checking out the branch syncs detached HEAD.
If branch <name> already exists from prior work,
checking it out switches away from the synced HEAD
and leaves the worktree out of sync.

Moving sync after git checkout ensures that the
actual checked out branch is synchronized.

Test: Added test_add_with_sync_order and ran manual test commands.

Original-Original-Bug: 516876349
TAG: agy
CONV: 54ba228b-0a73-4dfa-8c3d-43d8babca281
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1674670
Original-Original-Revision: ec8849c32b8927799b8a624f9e8437e6e3c37519
GitOrigin-RevId: b51550414ff39c28b1e20f25116f5b61b112c425
Change-Id: I035e8081e390a0bb54a46b0b3eeb072dd29fc689
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1675082
Cr-Commit-Position: refs/heads/main@{#195380}

stem

diff --git a/stem b/stem
index 63a4f71..5ff928f 100644
--- a/stem
+++ b/stem
@@ -8,6 +8,6 @@
             manifest="manifests/platform"
             root=""
             remote="https://fuchsia.googlesource.com/fuchsia"
-            revision="5a39066c0a000450bb69a893f32c121ff987fc16"/>
+            revision="ec8849c32b8927799b8a624f9e8437e6e3c37519"/>
   </imports>
 </manifest>