[TwigBundle] properly set request attributes in controller test

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        |
this change is wrong. It won't display the full exception template in debug mode when the original format was not HTML.

However, it should use ``$showException``, not ``$this->debug``