infoschema: fix bug when apply rename table diff

[alivxxx]

What have you changed? (mandatory)

In order to fix the data race in #7318, we copy the DBInfo before write. However, when applying the RenameTable diff for the same schema, we would:

• First, copy the schema into dbInfo
• Then, copy the schema into oldDBInfo, drop the table in it, and this would be the final DBInfo in the infomation schema.
• Last, add the table in dbInfo, although it no longer takes effects.

In order to fix it, we need to not copy the DBInfo twice for the same schema.

What is the type of the changes? (mandatory)

• Bug fix (non-breaking change which fixes an issue)

How has this PR been tested? (mandatory)

Unit test.

Does this PR affect documentation (docs/docs-cn) update? (mandatory)

No.

Does this PR affect tidb-ansible update? (mandatory)

No.

Does this PR need to be added to the release notes? (mandatory)

No.

Refer to a related PR or issue link (optional)

Benchmark result if necessary (optional)

Add a few positive/negative examples (optional)

PTAL @coocood @zimulala @winoros

[coocood]

LGTM

[zz-jason]

LGTM

[zz-jason]

/run-all-tests