[rls_e2e_test] increase RPC timeout (grpc#37708)

I think this will fix the following flake:

https://btx.cloud.google.com/invocations/193ce9f4-2a6a-445b-b6a6-8b28dac14d21/targets/%2F%2Ftest%2Fcpp%2Fend2end:rls_end2end_test;config=213e6770efdd9d7e0a9867560d39d4ea0067b835bad2334b239f96b3b6b502ba/tests

Closes grpc#37708

COPYBARA_INTEGRATE_REVIEW=grpc#37708 from markdroth:rls_e2e_flake_fix a7c8272
PiperOrigin-RevId: 674034919

test/cpp/end2end/rls_end2end_test.cc

@@ -234,7 +234,7 @@ class RlsEnd2endTest : public ::testing::Test {
   }
 
   struct RpcOptions {
-    int timeout_ms = 2000;
+    int timeout_ms = 5000;
     bool wait_for_ready = false;
     std::vector<std::pair<std::string, std::string>> metadata;
 
@@ -922,14 +922,15 @@ TEST_F(RlsEnd2endTest, RlsRequestTimeout) {
           .set_default_target(grpc_core::LocalIpUri(backends_[1]->port_))
           .set_lookup_service_timeout(grpc_core::Duration::Seconds(2))
           .Build());
-  // RLS server will send a response, but it's longer than the timeout.
+  // RLS server will send a response, but it takes longer than the
+  // timeout set in the LB policy config.
   rls_server_->service_.SetResponse(
       BuildRlsRequest({{kTestKey, kTestValue}}),
       BuildRlsResponse({grpc_core::LocalIpUri(backends_[0]->port_)}),
       /*response_delay=*/grpc_core::Duration::Seconds(3));
   // The data plane RPC should be sent to the default target.
-  CheckRpcSendOk(DEBUG_LOCATION, RpcOptions().set_timeout_ms(4000).set_metadata(
-                                     {{"key1", kTestValue}}));
+  CheckRpcSendOk(DEBUG_LOCATION,
+                 RpcOptions().set_metadata({{"key1", kTestValue}}));
   EXPECT_EQ(rls_server_->service_.request_count(), 1);
   EXPECT_EQ(backends_[0]->service_.request_count(), 0);
   EXPECT_EQ(backends_[1]->service_.request_count(), 1);