ddl: fix alter column set default wrongly updates the schema (#32249)

[ti-srebot]

cherry-pick #32249 to release-5.3
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/32264

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/32264:release-5.3-6d2ad99ce339

---

Signed-off-by: wjhuang2016 huangwenjun1997@gmail.com

What problem does this PR solve?

Issue Number: close #31074

Problem Summary:
Should use the new column to update the default, not in place.

What is changed and how it works?

clone the old column.

Check List

Tests

• Unit test
• Integration test
  This case is covered by schrddl.
• Manual test (add detailed scripts or steps below)
  Modify code to sleep before adding the job into the queue, and check if its default is changed.

create table gf(a int);
alter table gf alter column  a set default 13;

• 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

fix `alter column set default` wrongly updates the schema

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Defined2014
• hawkingrei

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[ti-srebot]

/run-all-tests

[ti-srebot]

@wjhuang2016 you're already a collaborator in bot's repo.

[guo-shaoge]

@wjhuang2016 merge remainder~

[guo-shaoge]

/run-mysql-test

[purelind]

/run-mysql-test

[guo-shaoge]

/merge

[ti-chi-bot]

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

Commit hash: 2e227ac