[ez][c10d] change ERROR to WARNING (#134349)

Summary:
Change error to warning because TCPStore can be torn down during a normal shutdown. It's OK if we're unable to access TCPStore. Should not be an error.

Test Plan:
Ran locally

Pull Request resolved: https://github.com/pytorch/pytorch/pull/134349
Approved by: https://github.com/fduwjj, https://github.com/wconstab

torch/csrc/distributed/c10d/ProcessGroupNCCL.cpp

@@ -1399,7 +1399,7 @@ void ProcessGroupNCCL::heartbeatMonitor() {
           checkExceptionDump =
               globalStore_->check({std::string(EXCEPTION_DUMP)});
         } catch (const std::exception& e) {
-          LOG(ERROR)
+          LOG(WARNING)
               << logPrefix()
               << "Failed to check the \"should dump\" flag on TCPStore, "
               << "(maybe TCPStore server has shut down too early), with error: "