[test] Increase timeout in pre_stop_hook_server_test (#37126)

Closes #37126

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37126 from eugeneo:increase-timeout-hook-test 190cd3d60c
PiperOrigin-RevId: 648415617

test/cpp/interop/pre_stop_hook_server_test.cc

@@ -209,7 +209,8 @@ TEST(PreStopHookService, StartDoRequestStop) {
   stub.async()->Hook(
       &infos[1].context, &infos[1].request, &infos[1].response,
       [&infos](const Status& status) { infos[1].SetStatus(status); });
-  ASSERT_TRUE(service.TestOnlyExpectRequests(2, absl::Milliseconds(100)));
+  ASSERT_TRUE(service.TestOnlyExpectRequests(
+      2, absl::Milliseconds(500) * grpc_test_slowdown_factor()));
   ClientContext ctx;
   SetReturnStatusRequest request;
   request.set_grpc_code_to_return(StatusCode::INTERNAL);
@@ -238,7 +239,8 @@ TEST(PreStopHookService, StartDoRequestStop) {
   stub.async()->Hook(
       &call_hangs.context, &call_hangs.request, &call_hangs.response,
       [&](const Status& status) { call_hangs.SetStatus(status); });
-  ASSERT_TRUE(service.TestOnlyExpectRequests(1, absl::Milliseconds(100)));
+  ASSERT_TRUE(service.TestOnlyExpectRequests(
+      1, absl::Milliseconds(500) * grpc_test_slowdown_factor()));
   status = call_hangs.WaitForStatus(absl::Milliseconds(100));
   EXPECT_FALSE(status.has_value()) << status->error_message();
   service.Stop();