ObjPtr<>-ify ClassLinker::FindClass(), fix 1 stale reference use.

Thread::CreateAnnotatedStackTrace() was using a stale
reference `aste_array_class`.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: I191907c0053456bb57de425aa6ccd9668df818a2
diff --git a/runtime/interpreter/unstarted_runtime_test.cc b/runtime/interpreter/unstarted_runtime_test.cc
index 88cfafb..fee8375 100644
--- a/runtime/interpreter/unstarted_runtime_test.cc
+++ b/runtime/interpreter/unstarted_runtime_test.cc
@@ -196,7 +196,7 @@
   // Prepare for aborts. Aborts assume that the exception class is already resolved, as the
   // loading code doesn't work under transactions.
   void PrepareForAborts() REQUIRES_SHARED(Locks::mutator_lock_) {
-    mirror::Object* result = Runtime::Current()->GetClassLinker()->FindClass(
+    ObjPtr<mirror::Object> result = Runtime::Current()->GetClassLinker()->FindClass(
         Thread::Current(),
         Transaction::kAbortExceptionSignature,
         ScopedNullHandle<mirror::ClassLoader>());