Fix outdated statement about TiDB's default transaction mode in optimistic-transaction.md

[hfxsd]

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• This PR is translated from:Fix outdated statement about TiDB's default transaction mode in optimistic-transaction.md docs#21921
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[yahonda]

While I need to use some translator to review this document, this statement also does not look like valid anymore

为了降低应用改造难度，TiDB 提供了数据库内部自动重试机制。
(To reduce the difficulty of application migration, TiDB provides an internal automatic retry mechanism.)

Since automatic retry of transactions is disabled by default and it is not recommended anymore.
https://docs.pingcap.com/tidb/stable/transaction-isolation-levels/

Starting from TiDB v3.0, the automatic retry of transactions is disabled by default. It is not recommended to enable the automatic retry because it might break the transaction isolation level. Refer to Transaction Retry for details.

[lilin90]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-10-16 09:23:54.172920285 +0000 UTC m=+345340.250172835: ☑️ agreed by lilin90.

[hfxsd]

@yahonda Thanks for the comment. I added a note to the automatic retry section. You can refer to the English PR pingcap/docs#21927

[lilin90]

New updates LGTM.

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[hfxsd]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #21010.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #21011.