Fix build with -Wrange-loop-construct (#13273)

Summary:
db/db_impl/db_impl_write.cc:208:19: error: loop variable '[cf_id, stat]' creates a copy from type 'const value_type' (aka 'const pair<const unsigned int, rocksdb::WriteBatchWithIndex::CFStat>') [-Werror,-Wrange-loop-construct]
  208 |   for (const auto [cf_id, stat] : wbwi->GetCFStats()) {
      |                   ^
db/db_impl/db_impl_write.cc:208:8: note: use reference type 'const value_type &' (aka 'const pair<const unsigned int, rocksdb::WriteBatchWithIndex::CFStat> &') to prevent copying
  208 |   for (const auto [cf_id, stat] : wbwi->GetCFStats()) {
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~
      |                   &
1 error generated.

Pull Request resolved: #13273

Reviewed By: jaykorean

Differential Revision: D68109780

Pulled By: cbi42

fbshipit-source-id: a0bc86bb82e8eaf7175c9cae4ae5dbad4f461d8c

Author: sunpoet

db/db_impl/db_impl_write.cc

@@ -205,7 +205,7 @@ Status DBImpl::IngestWBWI(std::shared_ptr<WriteBatchWithIndex> wbwi,
   ColumnFamilySet* cf_set = versions_->GetColumnFamilySet();
 
   // Create WBWIMemTables
-  for (const auto [cf_id, stat] : wbwi->GetCFStats()) {
+  for (const auto& [cf_id, stat] : wbwi->GetCFStats()) {
     ColumnFamilyData* cfd = cf_set->GetColumnFamily(cf_id);
     if (!cfd) {
       if (ignore_missing_cf) {