[VL] Fix bug where session config is lost when benchmark is enabled (#…

…5054)

It's a quick bug fix.

unordered_map::merge removes the duplicated items from source.

cpp/velox/compute/VeloxRuntime.cc

@@ -220,7 +220,10 @@ std::unique_ptr<ColumnarBatchSerializer> VeloxRuntime::createColumnarBatchSerial
 void VeloxRuntime::dumpConf(const std::string& path) {
   auto backendConf = VeloxBackend::get()->getBackendConf();
   auto allConf = backendConf;
-  allConf.merge(confMap_);
+
+  for (const auto& pair : confMap_) {
+    allConf.insert_or_assign(pair.first, pair.second);
+  }
 
   // Open file "velox.conf" for writing, automatically creating it if it doesn't exist,
   // or overwriting it if it does.