Fix callback.data nullable mismatch between model and DB schema

[vincbeck]

The model property data from callback mismatches its DB schema definition. This property should be nullable. This is reported by the test test_database_schema_and_sqlalchemy_model_are_in_sync when SQLA2 is used. This test is failing in #56212 and I fixed it and now cherry-picking from there.

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[ramitkataria]

This was my mistake 😅 I changed data from nullable to non-nullable but forgot to change it in the migration script. It is supposed to be non-nullable. There was another issue (about setting primary key constraint) I found in the 91 migration script so I can create a PR to fix both issues if you'd like

[ramitkataria]

I created this PR: 57836

[ferruzzi]

Commenting to block accidental merge. See Ramit's comments above.

The other PR is better

[vincbeck]

Closing this one in favor of #57836