Cherry-pick: Fix MSSQL index names with dashes not quoted (#1608)

## Upstream PR
https://github.com/dimitri/pgloader/pull/1608

## Summary
MSSQL index names containing dashes caused errors during migration. Fix applies `apply-identifier-case` to the `index-name` variable before constructing the `make-index` struct.

## Files
- `src/sources/mssql/mssql-schema.lisp`

## Notes
- Low risk, 1-line change
- **Priority: Medium**