ddl: fix cancel the rollbacking back may lead to meta data broken

[wjhuang2016]

What problem does this PR solve?

Issue Number: close #44143

Problem Summary:
It doesn't Unmarshal the rawArg to Arg if the job is rollbacking.

What is changed and how it works?

Don't update the RawArg since it doesn't change during cancel/pause/resume.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

fix cancel the rollbacking back may lead to meta data broken

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• tangenta
• zimulala

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[zimulala]

LGTM

[wjhuang2016]

/merge

[ti-chi-bot]

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

Commit hash: 9668164

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #44151.