[fixit] Increase sleep time for test `ProxyEnd2endTest.RpcDeadlineExpires` to reduce flakiness (#30631)

* Increase sleep time for test `ProxyEnd2endTest.RpcDeadlineExpires`

* Update

test/cpp/end2end/end2end_test.cc

@@ -1561,15 +1561,15 @@ TEST_P(ProxyEnd2endTest, RpcDeadlineExpires) {
   EchoResponse response;
   request.set_message("Hello");
   request.mutable_param()->set_skip_cancelled_check(true);
-  // Let server sleep for 40 ms first to guarantee expiry.
-  // 40 ms might seem a bit extreme but the timer manager would have been just
+  // Let server sleep for 4 secs first to guarantee expiry.
+  // 4 secs might seem a bit extreme but the timer manager would have been just
   // initialized (when ResetStub() was called) and there are some warmup costs
   // i.e the timer thread many not have even started. There might also be other
   // delays in the timer manager thread (in acquiring locks, timer data
   // structure manipulations, starting backup timer threads) that add to the
-  // delays. 40ms is still not enough in some cases but this significantly
-  // reduces the test flakes
-  request.mutable_param()->set_server_sleep_us(40 * 1000);
+  // delays. 4 secs might be still not enough in some cases but this
+  // significantly reduces the test flakes
+  request.mutable_param()->set_server_sleep_us(4 * 1000 * 1000);
 
   ClientContext context;
   std::chrono::system_clock::time_point deadline =