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/verifier/method_verifier_test.cc b/runtime/verifier/method_verifier_test.cc
index db3f093..d1be9fa 100644
--- a/runtime/verifier/method_verifier_test.cc
+++ b/runtime/verifier/method_verifier_test.cc
@@ -37,7 +37,7 @@
       REQUIRES_SHARED(Locks::mutator_lock_) {
     ASSERT_TRUE(descriptor != nullptr);
     Thread* self = Thread::Current();
-    mirror::Class* klass = class_linker_->FindSystemClass(self, descriptor.c_str());
+    ObjPtr<mirror::Class> klass = class_linker_->FindSystemClass(self, descriptor.c_str());
 
     // Verify the class
     std::string error_msg;