Changes

chore(tiflow): update MySQL version for sync-diff-inspector (#3978)

After upgrading the pod for sync-diff-inspector integration test in
https://github.com/PingCAP-QE/ci/pull/3971, it always failed due to
MySQL connection error.

The error is caused by SSL problem by lower verison of MySQL, so we
should upgrade it.

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Signed-off-by: Ruihao Chen <ruihao.chen@pingcap.cn>
 (commit: 3acfa28)