validation: put coins cache write log into bench debug log

src/validation.cpp

@@ -2029,8 +2029,8 @@ bool CChainState::FlushStateToDisk(
         }
         // Flush best chain related state. This can only be done if the blocks / block index write was also done.
         if (fDoFullFlush && !CoinsTip().GetBestBlock().IsNull()) {
-            LOG_TIME_SECONDS(strprintf("write coins cache to disk (%d coins, %.2fkB)",
-                coins_count, coins_mem_usage / 1000));
+            LOG_TIME_MILLIS_WITH_CATEGORY(strprintf("write coins cache to disk (%d coins, %.2fkB)",
+                coins_count, coins_mem_usage / 1000), BCLog::BENCH);
 
             // Typical Coin structures on disk are around 48 bytes in size.
             // Pushing a new one to the database can cause it to be written