Fix for text showplan

[aidanharan]

Fix for text showplan, which returns 2 result sets for single query. The multiple column headers were causing the following bug.

https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/actions/runs/9085233159/job/24968052134?pr=1173

ShowplanTestSQLServer::With SHOWPLAN_TEXT option#test_0001_use simple table printer:
RuntimeError: Wrapped undumpable exception for: ActiveRecord::StatementInvalid: NoMethodError: undefined method `-@' for an instance of Array
    /usr/local/bundle/bundler/gems/rails-1d681e341c01/activerecord/lib/active_record/result.rb:52:in `each'
    /usr/local/bundle/bundler/gems/rails-1d681e341c01/activerecord/lib/active_record/result.rb:52:in `initialize'
    /activerecord-sqlserver-adapter/lib/active_record/connection_adapters/sqlserver/database_statements.rb:437:in `new'
    /activerecord-sqlserver-adapter/lib/active_record/connection_adapters/sqlserver/database_statements.rb:437:in `handle_to_names_and_values'
    /activerecord-sqlserver-adapter/lib/active_record/connection_adapters/sqlserver/database_statements.rb:61:in `internal_exec_sql_query'