[source-MSSQL] MSSQL source columns prefixed with '_' are loaded as NULL in destination

### Connector Name

source-mssql

### Connector Version

Microsoft SQL Server (MSSQL) v5.0.0

### What step the error happened?

During the sync

### Relevant information

CREATE TABLE dbo.airbyte_bug_test (
id INT
);

INSERT INTO dbo.airbyte_bug_test
VALUES (1),(2),(3);

CREATE VIEW dbo.airbyte_bug_test_view AS
SELECT
id,
'UNDER' AS _test_under,
'NORMAL' AS test_normal
FROM dbo.airbyte_bug_test;

Expected:
id, _test_under, test_normal
1, UNDER, NORMAL
2, UNDER, NORMAL
3, UNDER, NORMAL

Actual:
id, _test_under, test_normal
1, NULL, NORMAL
2, NULL, NORMAL
3, NULL, NORMAL

Notes:

- Source query returns correct values for both columns.
- Airbyte sync completes successfully.
- Destination table contains values for test_normal.
- Destination table contains NULL for every row in _test_under.
- Renaming _test_under to x_test_under causes values to sync correctly.

### Relevant log output

```shell

```

### Contribute

- [ ] Yes, I want to contribute

---
**Internal Tracking:** https://github.com/airbytehq/oncall/issues/13016

Start with the source-mssql connector and reproduce the sync using the provided CREATE TABLE, view, and INSERT statements. Trace how the view columns are read and mapped, focusing on the leading-underscore column, then verify that _test_under contains UNDER rather than NULL while test_normal remains unchanged.

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