fix(mssql): cast sql_variant in query generator

[killerfurbel]

Pull Request check-list

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• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving? description see below
• Have you added new tests to prevent regressions?
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Description of change

sys.extended_properties.value is a column of type sql_variant. If used with msnodesqlv8, the driver will crash when executing this query without casting the sql_variant to nvarchar.

The issue is only relevant if a model is synced with {alter: true} option. In this case, the Application will just exit without any error. The "real" error is probably in the c++ driver of msnodesqlv8, since I was not able to debug it any further. However, I was able to isolate the query which is causing the bug. Running the same query without sequelize causes the same problem. I started modifying the query and found it that it is related to the extended_properties value column. Casting it to NVARCHAR solves the issue.

This is a really small fix. I tested it locally in my project. I don't want to install all the test environments. I think a new test would be overkill or impossible, since there is nothing to try/catch, since the application exits without any error! Please let me know what you think. I would be very happy if the change could be implemented.