[roll] Roll fuchsia [assembly] Add GN arg for verbose ffx assembly operation

Adds a new GN arg to enable verbose output from ffx assembly.

Adding the following to args.gn:
```
verbose_image_assembly = true
```

or adding the following to `fx set`:
```
fx set ... --args=verbose_image_assembly=true
```

Will enable all log output from the ffx assembly plugin to be output
by the assembly build action(s), instead of operating silently.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/550903
Original-Revision: c6f3e81e58d67d2e863d120bf81bffc6d9769d5c
GitOrigin-RevId: f6e5c29c480e8c58daf1b9f0fa989479b09d224e
Change-Id: Id4dd25af90c52d15a4114b185166214255b062b7
diff --git a/stem b/stem
index 66883ce..eb9ca20 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="d0fb1d4609e1f6b26ab1c222d0cc76620d0a6645"/>
+             revision="c6f3e81e58d67d2e863d120bf81bffc6d9769d5c"/>
   </projects>
   <hooks>
     <hook name="install-environment"