feedback-manager: Let app level cap important level

As per DBus spec the `important` hint is meant to override
the global feedback level not any per app level the user
might have configured as otherwise there's no way to override
this.

Closes: https://gitlab.freedesktop.org/agx/feedbackd/-/issues/93
Signed-off-by: Guido Günther <agx@sigxcpu.org>

src/fbd-feedback-manager.c

@@ -758,10 +758,11 @@ fbd_feedback_manager_get_effective_level (FbdFeedbackManager      *self,
   app_level = app_get_feedback_level (app_id);
   can_important = app_is_important (self, app_id);
 
-  if (important && can_important)
-    level = want_level;
-  else
+  if (important && can_important) {
+    level = MIN (want_level, app_level);
+  } else {
     level = get_max_level (self->level, app_level, want_level);
+  }
 
   return level;
 }