When translating SqlQueryRootExpression, the resulting SelectExpression's ColumnExpression (in _projectionMappings) has Type e.g. IQueryable<string> instead of string - this is an incorrect tree representation.

This triggered #33272, which was worked around by @cincuranet in #33580, but without addressing the actual root cause (which is an invalid tree). This surfaced again EFCore.PG where the workaround wasn't yet applied.