chore: update generate pdf scripts

[YiniXu9506]

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What is changed, added, or deleted? (Required)

Since the structure of TOC.md has been changed, the parse method for generating PDF is failed. This PR is to fix the parse method.

And this issue caused by #831

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

• master (the latest development version)
• v5.3 (TiDB DM 5.3 versions)
• v2.0 (TiDB DM 2.0 versions)
• v1.0 (TiDB DM 1.0 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:

• Liuxiaozhen12

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[Liuxiaozhen12]

/merge

[ti-chi-bot]

@Liuxiaozhen12: /merge in this pull request requires 2 approval(s).

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In response to this:

/merge

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[Liuxiaozhen12]

/remove-status LGT1
/status LGT2

[Liuxiaozhen12]

/merge

[ti-chi-bot]

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

Details

Commit hash: fe3d3ac

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #840.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #841.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #842.