scheduler: fix scheduler save config (#7108)

[ti-chi-bot]

This is an automated cherry-pick of #7108

What problem does this PR solve?

Issue Number: Close #6897

What is changed and how does it work?

Nowadays we have 2 configs setting way
We need to make sure that create just means create and not further save the configuration

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Release note

None.

[ti-chi-bot]

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• disksing

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[ti-chi-bot]

This pull request is closed because its related version has closed automatic cherry-picking.
If it's still needed, you can reopen it or just regenerate it using bot,
see:

https://prow.tidb.net/command-help#cherrypick
https://book.prow.tidb.net/#/plugins/cherrypicker