tiflash: fix config value of tidb_allow_mpp

[ran-huang]

What is changed, added or deleted? (Required)

Align the value with Chinese

Which TiDB version(s) do your changes apply to? (Required)

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By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• [x] master (the latest development version)
• [ ] v6.3 (TiDB 6.3 versions)
• [x] v6.1 (TiDB 6.1 versions)
• [ ] v5.4 (TiDB 5.4 versions)
• [ ] v5.3 (TiDB 5.3 versions)
• [ ] v5.2 (TiDB 5.2 versions)
• [ ] v5.1 (TiDB 5.1 versions)
• [ ] v5.0 (TiDB 5.0 versions)

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Do your changes match any of the following descriptions?

• [ ] Delete files
• [ ] Change aliases
• [ ] Need modification after applied to another branch
• [ ] Might cause conflicts after applied to another branch

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• shichun-0415

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[ran-huang]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 1abb311925452ab0dc78576ecfe97022adaf926e

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10743.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10744.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #10745.