[SYCL][Graph] Fix memory leak multithreading Finalize test

'queue::submit' function is not thread-safe.
Consequently, threads in Finalize test cannot safely submit their graph to the same queue (this generates sometimes memory leaks).
This commit updates this test so that each thread submits its graph to a differentes queue.

Author: mfrancepillois

sycl/test-e2e/Graph/Threading/finalize.cpp

@@ -46,10 +46,12 @@ int main() {
 
   Barrier SyncPoint{NumThreads};
 
+  std::vector<queue> SubmissionQueues(NumThreads);
   auto FinalizeGraph = [&](int ThreadNum) {
     SyncPoint.wait();
     auto GraphExec = Graph.finalize();
-    Queue.submit([&](sycl::handler &CGH) { CGH.ext_oneapi_graph(GraphExec); });
+    SubmissionQueues[ThreadNum].submit(
+        [&](sycl::handler &CGH) { CGH.ext_oneapi_graph(GraphExec); });
   };
 
   std::vector<std::thread> Threads;
@@ -63,7 +65,9 @@ int main() {
     Threads[i].join();
   }
 
-  Queue.wait_and_throw();
+  for (unsigned i = 0; i < NumThreads; ++i) {
+    SubmissionQueues[i].wait_and_throw();
+  }
 
   Queue.copy(PtrA, DataA.data(), Size);
   Queue.copy(PtrB, DataB.data(), Size);