Fix system_weak_test

A recent change made the SS collector send the Broadcast event. This
caused the system_weak_test to fail when run with this collector.

Test: ./art/test/testrunner/run_build_test_target.py -j30 art-gtest-debug-gc
Bug: 76205593
Change-Id: I8780492240453f51e40808241ed63c455485834e
diff --git a/runtime/gc/system_weak_test.cc b/runtime/gc/system_weak_test.cc
index 07725b9..dad1beb 100644
--- a/runtime/gc/system_weak_test.cc
+++ b/runtime/gc/system_weak_test.cc
@@ -112,6 +112,7 @@
   switch (type) {
     case CollectorType::kCollectorTypeCMS:
     case CollectorType::kCollectorTypeCC:
+    case CollectorType::kCollectorTypeSS:
       return true;
 
     default: