Don't print error log for indexLookUpExecutor when context canceled

[yibin87]

Enhancement

When indexLookUpExecutor is closed before its index/table worker finished(it may be caused by limit operator), it will use cancelFunc to inform index/tableWork. Currently, this will lead to useless error logs: "[2025/05/12 10:25:18.142 +08:00] [ERROR] [distsql.go:1572] ["table reader fetch next chunk failed"] [conn=2120221196] [session_alias=] [error="context canceled"]"

1. LimitExec returns nil when fetches enough rows, and its Close function will be called next:
   

   tidb/pkg/executor/select.go

   Lines 429 to 431 in 2503d50

   	if e.cursor >= e.end {
   	return nil
   	}

2. When indexLookUpExecutor's Close function is called, it will call its cancelFunc to inform index/tableWork:
   

   tidb/pkg/executor/distsql.go

   Lines 898 to 901 in 2503d50

   	if e.cancelFunc != nil {
   	e.cancelFunc()
   	e.cancelFunc = nil
   	}

3. In coprocessor, each time it tries to receive response, it checks the context status, and return error when context canceled:
   

   tidb/pkg/store/copr/coprocessor.go

   Lines 1130 to 1134 in 2503d50

   	resp, ok, closed = it.recvFromRespCh(ctx, it.respChan)
   	if !ok || closed {
   	it.actionOnExceed.close()
   	return nil, errors.Trace(ctx.Err())
   	}

4. In indexLookUpExecutor's tableWork, it outputs error log when errors returned from coprocessor:
   

   tidb/pkg/executor/distsql.go

   Lines 1564 to 1567 in 2503d50

   	if err != nil {
   	logutil.Logger(ctx).Error("table reader fetch next chunk failed", zap.Error(err))
   	return err
   	}