[18.0][FIX] base_external_dbsource_mssql: convert string query to TextClause expected by sqlalchemy

[JordiMForgeFlow]

The execute method expects as the query not a plain string, but an object. The easiest is to convert it to a TextClause object: https://docs.sqlalchemy.org/en/20/core/connections.html#sqlalchemy.engine.Connection.execute

Examples are actually provided in the documentation: https://docs.sqlalchemy.org/en/20/core/sqlelement.html#sqlalchemy.sql.expression.TextClause

[OCA-git-bot]

Hi @anddago78,
some modules you are maintaining are being modified, check this out!