Fix MySQL CAST AS TEXT regression

[kouz75]

With MySQL/MariaDB orderby failed.

A test have been replaced for bolt 6 :

  // Before (Bolt 5 / pre-DBAL v4) — correct:
  // TEXT→CHAR for everything EXCEPT SQLite → MySQL gets CHAR ✓                                                                                 
  if (! mb_strpos($backend_driver, 'sqlite') && $this->second === 'TEXT') {
      $this->second = 'CHAR';                                                                                                                   
  }                                                                                                                                           
                                                                                                                                                
  // After (Bolt 6.1.x) — regression:                                                                                                         
  // TEXT→CHAR ONLY for SQLite → MySQL gets TEXT ✗
  if ($platform instanceof SQLitePlatform && $this->second === 'TEXT') {                                                                        
      $this->second = 'CHAR';
  }                                                                                                                                             

to reproduce the bug:

Create the content type

  products:
      name: Products                                                                                                                            
      singular_name: Product
      title_format: "{title}-{subtitle}"                                                                                                        
      fields:                                                                                                                                 
          title:
              type: text
          subtitle:                                                                                                                             
              type: text

in a twig file

 {% setcontent allProducts = 'products' limit 200 orderby 'title' %}                                                                         
 {{ allProducts|length }}                                                                                                                      

you should have the error
Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'TEXT)), LOWER(value_21) FROM (SELECT b0_.id AS id_0, b0_.content_type AS content' at line 1")