Unstable UT TestGenerateTableSinkTaskWithBarrierTs in TiFlow

[hongyunyan]

What did you do?

run ut in ci

What did you expect to see?

run test success

What did you see instead?

Failed many times and succeeded sometimes.

Versions of the cluster

Upstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

(paste TiDB cluster version here)

Upstream TiKV version (execute tikv-server --version):

(paste TiKV version here)

TiCDC version (execute cdc version):

both master and 6.5

[fubinzh]

/severity moderate

[purelind]

also found this unstable ut on release-7.1

[asddongmen]

closed by #10770