Unstable test executor/asyncloaddata TestAsyncLoad

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

make failpoint-enable
cd executor/asyncloaddata
go test -tags intest -run TestAsyncLoad

2. What did you expect to see? (Required)

No error

3. What did you see instead (Required)

--- FAIL: TestAsyncLoad (27.91s)
    --- FAIL: TestAsyncLoad/TestInternalStatus (14.07s)
        show_test.go:284:
                Error Trace:    /home/genius/project/src/github.com/pingcap/tidb/executor/asyncloaddata/show_test.go:284
                                                        /home/genius/project/go/src/runtime/asm_amd64.s:1598
                Error:          "[]" should have 1 item(s), but has 0
                Test:           TestAsyncLoad/TestInternalStatus
FAIL
exit status 1
FAIL    github.com/pingcap/tidb/executor/asyncloaddata  27.967s

4. What is your TiDB version? (Required)

master 6273e22